US 3652975 A
A load break electrical connector assembly, including a bushing and a plug-in cable connector or termination. The bushing and plug-in cable connector include cooperative sleeve and rod members, respectively, formed of arc confining and extinguishing electrical insulating materials, with at least one of the cooperative insulating members being composed essentially of methyl methacrylate polymer, having a glass filter filler.
Claims available in
Description (OCR text may contain errors)
United States Patent Keto [451 ar. 28, 1972  ELECTRICAL CONNECTOR ASSEMBLY 3,513,437 5/1970 McMorris ..339/1 1 1 3,509,516 4/1970 Phillips ..339/1l1 X  Invent Augus sharpsv'ne 2,328,825 9/1943 McMahon ..200/149.1 x  Assignee: Westinghouse Electric Corporation, Pittg Primary Examiner-Richard E. Moore  Filed, Jam 9 1970 Attorney-A. T. Stratton, F. E. Browder and Donald R.
Lackey  Appl. No.: 1,827
 ABSTRACT  US. Cl ..339/11l A load break deal-km] connector assembly, including a bush ] Int. Cl ..H0lr 13/52 ing and a p|ug in Cable connector or termination The bushing  Field ofSearch ..200/l44.3, 149.1;339/111 and plug in cable connector include cooperative Sleeve and rod members, respectively, formed of arc confining and extin-  References Cited guishing electrical insulating materials, with at least one of the UNITED STATES PATENTS cooperative insulating members being composed essentially of 57 8 5/ 939 B 200/149 1 X methyl methacrylate polymer, having a glass filter tiller. 2, l5 1 oyer 3,242,257 3/1966 Jones et al ..200/144 C X 11 Claims, 1 Drawing Figure noz/ 6 PATENTwmzamz INVENTOR August I, Keto [(6t ATTORNEJV BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to electrical circuit interrupters, and more specifically to electrical connector assemblies of the type which have load break, load make, and fault close-in capabilities.
2. Description of the Prior Art The large increase in underground distribution of electrical power for residential usage has resulted in the development of dead front, plug-in type electrical cable connectors, including a plug-in shielded cable termination and bushing. The plug-in cable termination and bushing enable the high voltage shielded cables of the electrical distribution system to be quickly connected to, or disconnected from, electrical apparatus such as distribution transformers and electrical switches. The early plug-in cable connectors were non-load break devices, with the load break capability being supplied by auxiliary load break switches. While load break switches are acceptable functionally, they add substantially to the cost of the underground distribution system, and thus it would be desirable to provide a plug-in type electrical connector assembly which has load break capability. The term load break capability, as used in this specification, also signifies load make and fault close-in capabilities.
To provide a plug-in type electrical connector assembly with load break capability, and also fault close-in capability, the arc drawn upon breaking the load current must be quickly and effectively extinguished, and the arc and the gas pressures created when coupling the connector portions while a fault exists must be contained without catastrophic damage to the apparatus and without hazard to operating personnel. Since plug-in load break connectors of this type are used on systems with current limiting protection, such as fuses or circuit breakers, between the cable termination and the high voltage supply feeder, the fault close-in requirements of the bushing assembly may be predetermined.
Load break electrical connector assemblies must include means for interrupting the electrical are drawn between the separating electrical conductor portions of the plug-in cable connector and bushing, when the electrical connector assembly is disassembled while load current is flowing. This is accomplished in the prior art connectors by providing the plug-in cable connector and bushing with cooperative insulating sleeve and rod members, respectively, commonly referred to as the quench tube and snuffer rod, respectively, which members are formed of arc extinguishing materials. The quench tube and snuffer rod are disposed to confine and squeeze the are drawn between the separating electrical conductors, with the surfaces of the quench tube and snuffer rod decomposing under the influence of the hot arc, generating gases which cool, deionize and blow-out the arc. For example, copending application Ser. No. 771,707, filed Oct. 30, 1968, now abandoned, and refiled as a continuation-in-part application on Jan. 9, 1970, Ser. No. 1,828, discloses a bushing assembly having a quench tube formed of arc-extinguishing material, which application is assigned to the same assignee as the present application.
While the load break electrical connectors of the prior art are effective in extinguishing an are drawn when the connector is separated to interrupt load current, the products of decomposition, and resulting erosion, of the quench tube and snuffer rod, may seriously limit the number of load break operations the connector will withstand, and the ability of the connector to meet its fault close-in requirements may be impaired.
More specifically, while it is necessary for the quench tube and snuffer rod to decompose and thus erode, it should be a carefully controlled and slow erosion, the volume of gas generated should be adequate without being excessive to the point where the arc reignites after extinction, and the products of decomposition should not contain excessive amounts of conductive particles, such as free carbon, which particles deposit on the quench tube and snuffer rod and eventually destroy their ability to interrupt an arc. Excessive gas formation by the arc extinguishing materials under the influence of an arc may, on fault close-in, force the plug-in portion of the connector away from the bushing.
Therefore, it would be desirable to provide a new and improved load break electrical connector assembly which is able to repeatedly interrupt load currents and close properly on a fault, without excessive erosion of the arc extinguishing materials, withexcessive gas generation, and without producing conductive products of decomposition in amounts which will seriously impair the future ability of the connector to interrupt load current and close properly on a fault within the fault close-in rating.
SUMMARY OF THE INVENTION Briefly, the in vention is a new and improved circuit interrupter of the plug-in electrical connector type, having a plugin portion adapted for connection to shielded electrical cable, and a bushing assembly which is adapted for mounting on the casing of electrical apparatus, such as a distribution transformer. The connector assembly has load make and break, and fault close-in capabilities, provided by cooperative quench tube and snuffer rod members disposed in the plug-in and bushing portions of the connector, respectively, which members are formed of arc extinguishing materials. At least one of the cooperative arc quenching members is formed of methyl methacrylate polymer, which is filled with glass fibers, as this combination has been found to provide unexpected and superior results when used in cooperation with a member formed of the conventionally used arc extinguishing materials, and still better results when both the quench tube and snuffer rods are formed of a glass filled methyl methacrylate polymer. When one of the cooperative arc extinguishing members is formed of glass filled methyl methacrylate polymer, formation of free carbon is inhibited, the interruption of the load current is substantially quieter, and the amount of gas released is reduced without impairing the effectiveness of the connector in interrupting load current. The amount of erosion of the arc extinguishing materials is reduced, and the gas pressure which attempts to decouple the connector upon fault close-in, is also reduced, substantially increasing the life of the connector.
When both the quench tube and snuffer rod are formed of glass filled methyl methacrylate polymer, the products of decomposition are free of conductive particles, such as carbon, arc interruption is quiet, erosion is slow and gas release is adequate without being excessive, enabling the connector to repeatedly make and break load current, as well as close on faults, without substantially impairing its ability to function as rated.
BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description of exemplary embodiments thereof, taken in connection with the accompanying drawings, in which the single FIGURE is an elevational view, partially in section, of an electrical connector assembly having load make and break, and fault close-in capabilities, constructed according to the teachings of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawing, the single FIGURE is an elevational view, partially in section, of an electrical connector assembly 10 constructed according to the teachings of the invention. Electrical connector assembly 10, which is broadly an electrical circuit interrupter, includes first and second cooperative portions having first and second conductor means between which an electrical arc is formed, and, according to the teachings of the invention, are confining and extinguishing means is disposed to confine and extinguish an are drawn between the first and second conductors. More specifically, connector assembly M) includes a first portion including a plug-in cable connector 12, and a second portion including a bushing assembly 114, which, when assembled, provide a sealed electrical connection. The plug-in cable connector is adapted for connection to a shielded electrical cable, and bushing 14 is adapted for mounting through an opening in the casing of electrical apparatus, such as a distribution transformer.
Cable connector 112 includes a hood portion 16 and a main body portion 22, both formed of a resilient material such as an elastomer, with the hood portion 16 being molded to define a cavity 18 sized to snugly receive the upper portion of bushing 14. In other words, the plug-in cable connector and bushing portions have complementary surfaces, which enclose and seal an electrical connection made between their conductors. Cable connector 12 also includes an electrical conductor 20 which has one end connected to the conductor portion of a shielded electrical cable (not shown) within the main body portion 22 of the cable connector 12, and its other end extends coaxially into cavity 18. An insulating rod member 24, called the snuffer rod, is secured to the lower end of conductor 20, with both the conductor 20 and snuffer rod 24 having the same outside diameters at their junction, to provide a smooth transition from the insulating rod 24 to the conductor 20. The snuffer rod 24 is formed of an arc extinguishing material, as will be hereinafter explained. The lower end 26 of snuffer rod 24 may be curved or rounded to facilitate its introduction into the bushing assembly M. Conductor 20 may join the conductor of the shielded cable at a 90 angle, as shown, in which case connector 12 is commonly referred to as an elbow, or conductor 20 may be a coaxial continuation of the shielded conductor, as required by the specific application. A portion of the resilient housing of connector 12 may be formed of conductive material, such as conductive rubber, which is adapted to contact the shield of the shielded cable, and continue the cable shield to the casing of the apparatus when the connector is assembled with the bushing.
The bushing assembly 114 includes a cylindrical, elongated insulating body member 28 formed of a rigid solid insulating system, a conductive sleeve or tubular member 38, a terminal stud 32, a replaceable contact member 34, an insulating sleeve member 36, commonly called a quench tube, which is formed of arc confining and extinguishing material, as will be hereinafter explained, and a metallic mounting ring assembly 38.
The body member 28 has first and second ends M) and 42, respectively, with an aperture 44 extending between its ends. Body member 28 may be cast or molded of any suitable resinous insulation system which possesses the following characteristics. It must be a good electrical insulator, it must be weather resistant, crack resistant, rigid but not brittle, it must possess a high physical strength at ambient and elevated temperatures, and it must have a coefficient of thermal expansion which closely matches the coefiicient of thermal expansion of the tubular conductive member 30. Body member 28 is preferably cast, instead of molded, because of the superior strength of cast resinous insulation systems over molded systems. In general, the filled epoxy cast resin systems will provide the desired characteristics, with the filler being selected to match the coefficient of thermal expansion of the filled resin system to that of the metallic conductor or insert. A finely divided filler formed of beryllium aluminum silicate has been found to be excellent in matching the coefficient of thermal expansion of the filled epoxy resin system to copper, but other fillers may be used, such as quartz or silica. For 7,200 volt applications where the encased end of a bushing assembly is disposed in oil, or other insulating dielectric fluid, fillers for providing arc and track resistance are not required. If the encased end is to be operated in air, finely divided alumina trihydrate (Al,O '3H O) may be added to obtain the desired arc and track resistance.
Conductive sleeve member 30 is preferably formed of a thin wall tube, constructed of a good electrical conductor, such as 1 copper, with the tube having first and second ends 45 and 4 16, respectively, and an aperture 418. The aperture 88 has a uniform diameter except for a shoulder or step Sill which reduces the diameter of the aperture for a short longitudinal dimension, at a predetermined location intermediate the first and second ends 45 and 416, respectively, of the conductive sleeve member 30.
The wall of the aperture 48 is threaded, starting at the first end 45 of the conductive sleeve member 3E1) and extending to the location of shoulder 58. When using a thin wall tube, threads 52 in the inner diameter of the conductive sleeve member 30 may be obtained by rolling threads on the outside surface of the tube.
The second end 46 of conductive sleeve of tubular member 30 is hermetically sealed with a terminal stud 32, which is also formed of copper, or other good electrical conductor, and is adapted for connection to encased electrical apparatus, such as the high voltage winding of a distribution transformer. Terminal stud 32 includes a portion 54 having a diameter selected to snugly fit the diameter of aperture 68 of the conductive sleeve member 30, with portion 54 being secured within the aperture 48, such as by a silver solder bead, which electrically connects terminal stud 32 to conductive sleeve member 338, and also hermetically seals end 86 of conductive sleeve member '30. Portion 54 of terminal stud member 32 also includes an outwardly extending portion 56 which is adapted to receive an electrical lead and fastening means, such as a nut.
As illustrated in the figure, conductive sleeve member 38 is sealingly disposed in the aperture 44 of body member 28, with its first end 45 starting within the aperture M a predetermined dimension from the first end 40 of body member 28, and with its second end 456 being substantially aligned with the second end 42 of body member 28.
As will be hereinafter explained, the conductive sleeve member 30 is disposed within the casting mold and then the body member 28 is cast, to provide a seal between aperture M of body member 28 and the outer surface of conductive sleeve member 30.
The metallic mounting ring assembly 38 includes a flange portion 60 embedded within the cast body portion 28, an outwardly extending disc or ring portion 58, and a plurality of spaced extensions, such as extensions 62 and 6 3, which, along with the flange portion 60, extend toward the first end 410 of body member 28, and which have openings for receiving clips disposed on the cable termination to mechanically secure the cable connector 112 in assembled relation with the bushing M.
The embedded flange 68 of mounting ring member 38 extends upwardly from the disc or ring portion 58, toward the first end 40 of body member 28, forming a smooth cylindrical surface coaxial with the axis of the conductive sleeve member 30. The flange portion 60 may be of any suitable longitudinal length, and in addition to providing a strong mechanical bond with the body member 28, it also functions as a ground shield, providing a smooth equipotential surface which is connected to the metallic case or enclosure of the associated apparatus.
Mounting ring member 38 may be formed of any suitable material, such as steel, and it may be welded to the casing of the associated electrical apparatus. For example, bushing M may be inserted into an opening 66 in a metallic casing 68, with the ring portion 58 of the mounting ring member 38 resting against casing 68. The mounting ring member 38 may then be welded to the casing 68, as illustrated by the welding head 67. Or, if it is not desirable to permanently mount the bushing within an opening of its associated apparatus, a suitable gasket member (not shown) may be disposed between portion 58 of mounting member 38, and the casing 68, and the bushing M secured in place by a conventional spring and flange assembly (not shown), disposed on the encased end of the bushing M. A circumferential groove (not shown) may be disposed about body member 28 to receive the spring member of the spring and flange type mounting assembly.
In forming body member 28 of bushing 14, it is necessary to properly position the conductive sleeve member 30 and mounting ring member 38 within the casting mold, prior to the introduction of the casting resin system. In order to preclude an air leak between the inside of casing 68 and the atmosphere, about the embedded portion of the mounting ring member 38, due to non-adhesion of the cast resin system to the embedded portion of the mounting ring member 38, which may develop due to the welding heat if the ring member 58 is welded to the casing 68, or due to differences in the coefficients of thermal expansion of the mounting ring member 38 and the body member 28, a coating 70 of resilient material may be disposed on the flange 38. For example, as disclosed in copending application Ser. No. 821,371, filed May 2, 1969; now U.S. Pat. No. 3,504,106 which is assigned to the same assignee as the present application, the coating 70 may be a thermoplastic material, such as a linear, saturated polyester resin system. This material will adhere to the flange 60 and also the cast resin system, providing a hermetic seal between the mounting ring member 38 and cast body portion 28.
A coating 72 of material similar to the material of coating 70, may be disposed about the conductive sleeve member 30 for a predetermined longitudinal dimension, prior to its being embedded in the body member 28, in order to insure that an oil seal has been obtained between the conductive sleeve member 30 and body member 28. External threads, if provided, on the conductive tube member 30 will aid in obtaining a good air tight bond, but it has been found that when the encased end is disposed in oil, that oil may be forced between the conductive tube member 30 and body member 28 due to capillary action, even when air cannot be forced through the same path. Thus, coating 72 is additional protection against this occurrence. An elastomeric ring (not shown) disposed about conductive sleeve member 30 and embedded in the body member 28 may also be used to provide the seal, instead of coating 72. An elastomeric ring (now shown) may also be used in place of coating 70 on mounting ring member 38, by disposing the elastomeric ring about the upwardly extending portion offlange 70.
In casting body member 28, it is very important that the upwardly extending projection 74 of body member 28 be formed without a parting line. A parting line from the mold may score the inner wall of the elastomeric hood 16 of the plug-in cable connector 12 which snugly encompasses projection 74, and a sharp parting line may also cause electrical stress concentrations which may approach or exceed the corona point. The parting line may be eliminated between the first end 40 of body member 28 and shoulder 80, with shoulder 80 being the stop for the plug-in cable connector 12, by using an auxiliary mold member. The auxiliary mold member is shaped to form the length of the inside diameter of aperture 44 which starts at the first end 40 of body member 28 and extends to the first end 45 of conductive sleeve member 30, and it also forms the outside diameter of the projection 74 of body member 28. Mounting ring member 38 and conductive sleeve member 30 are disposed within the mold, and the auxiliary mold member is disposed on the first end 45 of the conductive sleeve member 30. The fluid casting insulation system forms the projection 74 by flowing upwardly to fill the cavity between the circumferentially continuous auxiliary mold member and the conductive sleeve member 30. The fluid casting insulation system is then gelled and cured to a high strength solid.
Bushing 14 thus includes a body member 28, a mounting ring 38, a conductive sleeve member 30, and a terminal stud member 32, which components are permanently assembled. The remaining components, i.e., contact member 34, and the arc confining and extinguishing tubular sleeve member 36 are all replaceable.
Contact member 34 is formed of a tubular conductor, such as copper, having an externally threaded portion 82 sized to cooperate with the threads 52 on the inside diameter of conductive sleeve member 30, and a pressure terminal portion 84 which has an outside diameter slightly smaller than the inside diameter of the conductive sleeve member 30, to provide a predetermined space between the pressure tenninal portion 84 and conductive sleeve member 30 when the threaded portion 82 is threadably engaged with the conductive sleeve member 30. Contact member 34 is inserted into the conductive sleeve member and rotated, using a tool designed for this purpose, until the end of the threaded portion is turned tightly against shoulder 50, to provide good electrical contact between contact member 34 and the conductive sleeve member 30.
The pressure terminal portion 84 of contact member 34 may be longitudinally slotted to provide a plurality of upwardly extending finger portions, which extend toward the first end 45 of conductive sleeve member 30 when assembled therewith, with the outside diameter of the pressure terminal portion 84 being reduced near its extreme end to receive a spring member 86 which is circumferentially disposed about the finger portions to maintain the desired inside diameter of the opening in the contact member 34, and provide a good tight electrical connection between the fingers and the electrical contact 20 of the cable connector 12, when the electrical contact 20 of the cable connector 12 extends into the opening defined by the inside surfaces of the contact fingers.
If the plug-in cable connector 12 is of the type which terminates the cable shield, with the ground return conductors of the cable being twisted together and connected to a suitable terminal on the casing 68, and corona extinction voltage within system requirements is obtained, the connector assembly 10 will not require means for continuing the cable shield to the casing 68. 1f the plug-in cable connector 12 is of the type which requires the bushing to continue the cable shield to the casing 66, a metallic coating 110, such as sprayed aluminum, may be disposed about the body member 28, starting between the shoulder and mounting ring member 26, and continuing along body member 28 for a predetermined dimension.
The quench tube member 36 has first and second ends 90 and 92, respectively, with its second end 92 terminating against, or a predetermined small dimension from the ends of the contact fingers on the pressure terminal 84. Quench tube member 36 has a plurality of threads 96 which cooperate with the internal threads 52 of conductive sleeve member 30. Adjacent the first end 45 of conductive sleeve member 311, the arc confining and extinguishing quench tube member 36 steps outwardly to a surface 98 which snugly fits the aperture 44 of insulating body member 28. The quench tube 36 again steps outwardly at the first end 40 of body member 28, providing a shoulder which rests against the first end 40 of body member 28, to limit the travel of quench tube 36 and properly locate its inner end 92 adjacent the pressure terminal portion 84 of contact member 34. The outer surface of quench tube 36 may then flare smoothly outward from the shoulder, and provide a smooth radius into its outer end 90, for receiving and cooperating with plug-in connector 12.
A sealant and lubricant, such as a silicon grease, should be used to insert quench tube 36 into cooperative engagement with conductive sleeve member 30, to seal the small clearance between quench tube 36 and the adjacent inner wall of the insulating body member 28 to prevent an arc from following this path to the outside surface of the bushing member 14, where it may proceed over the outer surface of the bushing to ground.
In the operation of electrical connector 10, the plug-in cable connector should be coupled with bushing 14 with a positive action which will bring the conductor 20 of the cable connector 12 into rapid, positive contact with the pressure terminal 84. If there is a fault in the apparatus of which connector is associated, or in its connected load, ionized gases produced by the resulting are between the conductors of connector l2 and bushing 14 will expand into a chamber 102. Chamber 102 is defined by the inside wall of conductive sleeve member 30, starting at the lower end 1104 of contact member 34, and terminating at end 103, a predetermined distance from end 104 of contact member 34. Excess volume within conductor sleeve member 30, from end 103 to terminal 32, is filled with means 105. Means 105 may be conductive or insulating, as desired. Chamber 102 is thus very important, as it provides space for ionized gases to expand, cool and condense. Without this expansion space, the expanding gases may force the plug-in cable connector 12 out of engagement with bushing M, with possible hazard to the operator. The surge or expansion chamber 102 also makes it unnecessary to vent the ionized gases to the inside of casing 68 through a one-way pressure release seal. Thus, the desired insulating level of the fluid dielectric disposed within casing 68 is maintained, and possible flashover within the casing from alive part to ground is also precluded, since ionized gas is not released to the inside of casing 68. The surge chamber 102 contains the ionized gases until they condense and cool, to reduce their vapor pressure. Any elevated pressure within chamber 1102 which remains following a close-in in which ionized gases are produced is inconsequential, as it will slowly equalize to atmospheric pressure, through the small clearance between the plug-in cable termination and the body member 28, and through pores in the insulation of which the cable connector 112 is formed. Further details of chamber 102, and its importance in the arc extinguishing process, are disclosed in copending application Ser. No. 1,828, filed Jan. 9, 1970, in the names of A. I. Keto and K. R. Klein, which is assigned to the same assignee as the present application.
If the fault in the load upon closing or coupling a cable connector with a bushing is of sufficient magnitude, i.e., a low impedance fault, the protective current limiting means, such as fuses or breakers, in the high voltage cable feeder will clear the circuit and limit the maximum current magnitude. Also, if a fault occurs after the plug-in cable connector 12 is coupled with bushing 141, the protective current limiting means will clear the circuit and there will be no danger to the operator when the cable connector 12 is removed from the bushing M. if the plug-in cable connector 12 is decoupled from the bushing 14 during normal load conditions, for example up to 200 amperes in a 7,200 volt circuit, an arc will be drawn between the ends of the contact fingers of the pressure terminal 04 and terminal of plug-in connector 12, with the are being drawn between the snuffer rod 24 and the quench tube 36. The heat of the arc will liberate deionizing gases from the snuffer rod 24 and quench tube 36, with the gases deionizing and blasting the arc to effect an early extinction thereof. Tests have shown that the arc drawn in a 7,200 volt circuit in which a load current of 200 amperes is flowing is extinguishing within one-half to 1 cycle.
in the arc extinction function, the snuffer rod 24 and quench tube 36 squeeze, stretch and cool the arc, as well as deionize and blast the arc by liberating gases. Therefore, the surfaces of the quench tube 36 and snuffer rod 24 adjacent the arc erode with each load break operation. In addition to liberating gases, conductive particles, such as free carbon are generated as a product of decomposition with the materials used in most prior art load break connectors. Cumulative erosion and contamination of the surfaces of the quench tube 36, and snuffer rod 24, as well as of surrounding surfaces of the bushing 14, increase the time required to extinguish the arc, until a point is reached where the connector will fail to interrupt the arc. The contamination due to conductive particles may produce pre-arcing upon closure of the connector, making it difficult to meet the fault close-in rating, such as a 10,000 ampere rating.
While liberation of gases is essential to the arc extinction function, the amount of gas liberated should not be so great that reignition of the arc occurs after extinction, and/or it results in such high gas pressure that connector 12 is blown back from the bushing 14 upon a fault close-in. Therefore, the materials of which the snuffer rod 24 and quench tube 36 are formed are of the utmost importance, if the electrical connector assembly 10 is to achieve the required number of load make and break operations and fault close-in capability. This invention discloses the use of a material for either the snuffer rod or quench tube, and preferably for both the snuffer rod and quench tube, which possesses many advantages over the materials used for these functions in the prior art. This material is methyl methacrylate polymer, which is filled with uniformly dispersed glass fibers. Methyl methacrylate polymer, without a glass fiber filler, is unsuitable, as it erodes rapidly and evolves an excessive amount of gas when subjected to the heat of an arc, resulting in reignition of the arc and failure to interrupt the arc. The glass fiber filler in the methyl methacrylate polymer not only makes the snuffer rod and quench tube mechanically stronger, it substantially reduces the erosion that occurs upon interrupting an arc, which substantially increases the useful life of the connector, it reduces the amount of gas formation while still providing adequate gas volume to blow out and deionize the arc, and it substantially reduces the amount of noise which occurs upon arc interruption. Further, the glass filled methyl methacrylate polymer produces no contaminating conductive by-products, such as free carbon, which eliminates the problem of pre-ignition on fault close-in due to contaminants, and substantially increases the number of load make-break cycles that the connector will satisfactorily perform.
The percentage of glass fiber filler is not critical, with satisfactory results being obtained with about l0 to 50 percent by weight of glass fiber, and about to 50 percent of methyl methacrylate polymer, with the preferred range of glass fiber being in the range of 20 to 30 percent, by weight. The length of the glass fibers and the outside diameter of the fibers, are not critical, as long as the length and diameter are such that they do not adversely affect uniform dispersion of the glass fibers throughout the polymer. All of the glass fibers should be in contact with the polymer, with this result being insured by pre-mixing or milling the polymer and glass fibers together at an elevated temperature, after which they are pelletized. The pellets may then be used in an injection molding process to form the snuffer rod and quench tube. The glass filled methyl methacrylate polymer may also be cast, if desired, to provide the snuffer rod and quench tube by casting into molds.
In the preferred embodiment of the invention, both the snuffer rod 24 and quench tube 36 are composed essentially of methyl methacrylate polymer, and a filler of glass fibers, as the products of decomposition are clean and free of carbon resulting in little or no contamination of the connector assembly, even after repeated load make-break operations. Thus, fault close-in is accomplished in a clean environment with no prearcing which could cause damage to the bushing and cable connector. Further, maximum life of the connector assembly 10 is assured, as erosion of the snuffer rod 241 and quench tube 36 is slow. However, advantages over the prior art electrical connectors are obtainable if only the snuffer rod, or only the quench tube is composed of methyl methacrylate polymer filled with glass fibers, with the other members being formed of the conventionally used prior art are quenching materials for these functions.
More specifically, if the quench tube 36 is composed of methyl methacrylate polymer filled with glass fibers, and the snuffer rod is composed of one of the polyamides (Nylon), the formation of free carbon is inhibited and reduced, reducing the chances of pre-arcing on fault close-in. The gas formation from this combination is adequate, without being excessive, providing satisfactorily load make and break operations, as well as fault close-in.
When using a quench tube formed of glass filled methyl methacrylate polymer and a snuffer rod formed of a high molecular weight polyoxylmethylene, such as disclosed in US. Pat. No. 3,059,081, the formation of free carbon is greatly reduced, and the load make-break, fault close-in operations are substantially quieter.
If the snuffer rod is composed of glass filled methyl methacrylate polymer, and the quench tube is formed of materials such as a high molecular weight polyoxylmethylene, or an unfilled acrylic, the glass filled methyl methacrylate polymer snuffer rod produces a quieting effect during load make-break and fault close-in, and it inhibits the formation of free carbon.
In summary, there has beendisclosed a new and improved load break type electrical connector assembly, which may be safely coupled and decoupled when the bushing assembly is connected to a load, and the load break bushing assembly may be connected to an energized cable termination when a fault of predetermined magnitude exists in the load connected to the bushing. The magnitude of the fault current is limited to a predetermined maximum magnitude by current limiting means associated with the primary supply circuit. The hot ionized gases produced when closing or coupling the connector to a fault, expand into a surge chamber formed in the conductive sleeve member, with the gases being confined within this chamber until they are cooled and condensed. The snuffer rod and quench tube members of the cable connector and bushing, respectively, are formed of arc extinguishing materials, and are disposed to squeeze and confine "an are drawn between the electrical conductors of the cable connector and bushing. At least one of the cooperative arc extinguishing members is composed of glass filled methyl methacrylate polymer, and preferably both are formed of this material, resulting in little or no free carbon being generated in the products of combustion, less erosion of the arc extinguishing members, a controlled gas generation which prevents reignition of the arc after extinction, it promotes quieter arc interruption, it eliminates pre-arcing on fault close-in due to conductive contaminants, thus extending the useful operating life ofthe connector assembly.
I claim as my invention:
1. An electrical circuit interrupter comprising:
first and second conductor means between which an electrical arc is formed,
arc confining and extinguishing means disposed to confine and extinguish an are drawn between said first and second conductor means, said arc confining and extinguishing means comprising a body including methyl methacrylate polymer and a filler ofglass fibers.
2. The electrical circuit interrupter of claim 1 wherein the arc confining and extinguishing means includes cooperative insulating rod and tube members disposed to squeeze an are formed between the first and second conductor means, with at least one of the cooperative insulating members including methyl methacrylate polymer filled with glass fibers.
3. The electrical circuit interrupter of claim 2 wherein both the cooperative insulating rod and tube members include methyl methacrylate polymer filled with glass fibers.
4. The electrical circuit interrupter of claim ll wherein the body comprises about to 50 percent by weight of glass fibers.
5. The electrical circuit interrupter of claim 1 wherein the first and second conductor means are disposed in a plug-in type cable connector and bushing assembly, respectively, with the cable connector and bushing assembly having complementary surfaces which confine and seal the electrical connection between the first and second electrical conductors, when the cable connector and bushing assembly are in assembled relatron.
6. A load break bushing assembly adapted to receive a plugin cable connector, comprising: an insulating body member, an electrical conductor disposed in said body member having a terminal adapted to contact the conductor of the plug-in cable connector, and a tubular arc confining and extinguishing member disposed to surround an are formed between said electrical conductor and the conductor of the plug-in connector, said tubular arc confining and extinguishing member including methyl methacrylate polymer and a filler of glass fibers. 7. The load break bushing assembly of claim 6 wherein the tubular arc confining and extinguishing member includes about 10 to 50 percent, by weight, of glass fiber tiller 8. A load break bushing assembly adapted to receive a plugin cable connector, comprising:
an elongated body member formed of a cast resinous insulation, said body member having first and second ends and an aperture which extends between its ends,
a tubular conductive member having first and second ends and an aperture which extends between its ends, said tubular conductive member being disposed in the aperture of said body member with its first end spaced from the first end of said body member,
a contact member having a pressure terminal disposed at one end thereof, said contact member being removably disposed in the aperture of said tubular conductive member,
and a tubular arc confining and extinguishing member removably disposed in the aperture of said insulating body member at its first end, said tubular arc confining and extinguishing member including methyl methacrylate polymer and a filler of glass fibers.
9. The load break bushing assembly of claim 8 wherein the glass fiber filler is in the range of about 10 to 50 percent by weight.
10. A cable connector adapted to make a sealed electrical connection by plugging into a bushing assembly, comprising:
an electrical conductor having a first end adapted for connection to an electrical cable, and a second end adapted to enter a pressure terminal contact of a bushing assembly,
insulating means disposed about said electrical conductor,
. said insulating means defining a cavity into which the second end of said electrical conductor projects,
and an insulating rod member fixed to the second end of said electrical conductor, said insulating rod member including methyl methacrylate polymer and a filler of glass fibers.
11. The cable connector of claim 10 wherein the insulating rod member includes about 10 to 50 percent glass fiber filler by weight, and about to 50 percent methyl methacrylate polymer by weight.