US3686603A

US3686603A - Electrical connector

Info

Publication number: US3686603A
Application number: US820370A
Authority: US
Inventors: Arthur M Lockie; Merrill G Leonard
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-04-30
Filing date: 1969-04-30
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: CA924760A

Abstract

A fusible plug-in type electrical connector for interconnecting a shielded electrical conductor with a load circuit. The removable plug-in portion of the connector includes means for reducing the electrical stress adjacent the electrodes of the fuse, one of which is still at line potential after the fuse has interrupted the circuit.

Description

United States Patent Lockie et a1.

1541 ELECTRICAL CONNECTOR [72] Inventors: Arthur Lockie, Sharpsville, Pa.; I

Merrill G. Leonard, Fowler, Ohio [73] Assignee: Westinghouse Electric Corporation,

' Pittsburgh, Pa.

[22] Filed: April 30, 1969 21 A l. No.2 820,370

52 us. c1 ..337/2o1',337/224 51 Int. Cl.....l-l0lh 85/02, H01h 85/22, 1101: 13/46 [58] Field of Search .."..174/73; 337/191, 192, 193, 3 337/197, 201, 205, 224, 263; 389/45, 59,60,

[56] References Cited UNITED STATES PATENTS 3,513,425. 5/1970 Arndt ..337/201 10/1967 Leonard et a1 ..337/205 X 1451 Aug. 22, 1972 3,307,137 2/1967 Tordoff et a1 ..l74/73 X 3,116,386 12/1963 Sperzel ..339 59x 2,593,426 4/1952 Fahnoe.....- ..337/224 FOREIGN PATENTS OR APPLICATIONS 828,861 2/1960 Great Britain ..337/224 Primary ExaminerBemard A; Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-A. T, Statton, F. E. Browder and D. R. Lackey 57 ABSTRACT A fusible plugintype electricalconnector for interconnecting a shielded electrical conductor with a load circuit. The removable plug-in portion of the connector includes means for reducing the electrical stress adjacent the electrodes of the fuse, one of which is still at line potential after the fuse has interrupted the Patented Au 22,1972 I 3,686,603

2 Sheets-Sheet 1 WITNESSES INVENTORS Arthur M. Lockie and W BY Merrill G. Leonard film 6. Z2

ATTORNEY Patented Aug. 22, 1972 3,686,603

2 Sheets-Sheet 2 1 ELECTRICAL CONNECTOR I BACKGROUND OF THE INVENTION 2, 1968, now US. Pat. No. 3,512,118, which is assigned to the same assignee as the present application, discloses a new and improved electrical connector which connects a shielded electrical cable to a load circuit via a current limiting fuse disposedin a load-break disconnect. The current limiting fuse limits the power dissipated at the separable contacts of the disconnect, in the event the disconnect is operated under fault conditions. a

While the current limiting fuse accomplishes the I desired function, corona, which may cause erosion, burning or tracking, hasbeen observed on the inside surface of the fuse holder, after the fuse interrupts a fault. I

SUMMARY OF THE INVENTION Briefly, the present invention is anew and improved fusible plug-in type electrical connector or disconnect, which solves the problem of the prior art, wherein the inside surface of the fuse holding portion of the connector is attacked following-a circuit interruption by the fuse.

In normal operation, with the fusible element of the fuse intact, all of the internal metallic parts of the fuse, fuse holder, and connector, are virtually at the same electrical potential, i.e., that of the central conductor of the cable to which the connector is attached. The conductive, or semiconductive outer surface of the connector, however, is connected to the grounded outer sheath of the cable. Thus, a high electrical stress exists between the internal metal parts and the outer surface of the connector. If this stress were to be applied to any air within the connector, it would produce corona which would damage the connector and/or produce radio interference.

A similar situation occurs in conventional plug-in connectors which do not contain fuses. In the nonfused connector, it is common practice to line the inner surface of the connector insulation with conductive material which is connected to the internal metal parts. This construction removes the electrical stress from the air inside the connector, and corona is minimized or eliminated.

This construction, however, cannot be applied to fusible connectors. When the fusible element of a fuse -in a fusible connector melts, due toa faultin the load circuit, the internal metal parts at the load end of the fuse assume ground potential, while those at the opposite end remain at line potential. If conductive material was used to line the inner wall of the fuse chamber, it would bridge the fuse insulation, and the fuse could not perform its intended function of disconnecting a fault from the line. Providing a simple discontinuity in the conductive liner would notsolve the problem, since Iine-to-ground potential would appear across the discontinuity when the fusible melts, metals causing corona in the adjacent air.

' resilient member.

With this realization, a new and improved fusible electrical connector is provided which reduces the voltage gradient and the maximum stress adjacent one, or

both, electrodes of the fuse, following a circuit interruption. In one embodiment of the invention, a material having a voltage dependent resistivity is disposed on the inner annular surface of the connector surrounding the electrode of the fuse which is still at line potential following the circuit interruption. This coating may be electrically connected to the live Contact of the 'Con-' nector. A similar coating may be applied adjacent the other electrode of the fuse, if necessary.

In another embodiment, a resilient insulating liner is disposed between the live electrode of the fuse and the wall of the fuse-chamber, to exclude air from this highly stressed area. This embodiment may be used in combination with a conductive, or semiconductive shield or coating disposed between the liner and the wall of the fuse chamber, with the shield being applied directly to the wall of the fuse holder, or being a part of the In still another embodiment, the fuse electrode which is still at line potential following a circuit interruption is constructed with a smaller outside diameter than the insulating bodyiportion of the fuse,-and' themating contact of the connector has substantially this same small diameter, to increase the clearance between the fuse electrode and the wall of the fuse chamber, as well as to dispose the insulating body portion of the fuse between the fuse electrode and the wall portion of the fuse chamber.

BRIEF DESCRIPTION OF THE DRAWINGS 1 Further advantages and uses of the invention will becomemore apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is an elevational view, partially 'in section, of a new and improvedfusible electrical connector of the plug-in type, constructed according to a first embodiment of the invention;

FIG. 2 is a fragmentary elevational view, partially in section, of the connector shown in FIG. 1, constructed according to another embodiment of the invention; and

FIG. 3 is a fragmentary elevational view, partially in section, of the connector shown in FIG. 1, constructed according to still another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The recent emphasis on underground electrical distribution for residential users, has developed the need for moisture-proof connectors which may be quickly and safely operated to interconnect, or disconnect, a shielded cable and a load circuit. The hereinbefore mentioned copending application discloses such a connector or disconnect, with a current limiting fuse being used to limit the power dissipated at the contacts of the connector, in the event an attempt is made to connect the energized electrical cable to a load circuit having a fault thereon. While the current limiting fuse performs the function for which it was intended, it has been found that erosion or tracking occurs on the inner annular surface of the fuse chamber adjacent the electrode of the fuse which remains at line potential following a circuit interruption by the fuse.

Removing the grounded shieldfrom the cableand fuse holder may solve this problem,1as the electrostatic field would expand into a much larger area, reducing the stress around the live fuse electrode. Even here, however, if the distance between the electrode and inside wall of the fuse holder is small, excessive stress may still be created. If the shield is removed only from the connector, the shield on the cable is terminated in a stress cone, and a large clearance is provided between the electrode and the inside wall of the fuse holder, the damage to the fuse holder may be eliminated. However, both of these solutions are theoretical, and would not be tolerated in actual practice as a continuous shield extending over both the cable and fuse holder is preferred for safety reasons.

The present invention solves this problem of the prior art, while maintaining the grounded shield on the cable and the fuse holder. More specifically, FIG. 1 is v an elevational view, partially in section, of a new and improved electrical connector constructed according to the teachings of a first embodiment of the invention. Connector 10 includes a removable plug-in member 12, and a stationary member 14. The plug-in member 12 is electrically connected to a shielded electrical cable 16, which in turn is connected to a source (not shown) of electrical potential. The stationary member 14 is electrically connected to a load circuit, such as a distribution transformer. Thus, stationary member 14 may perform the function of an insulating bushing, being mounted in sealed relation through an opening 18 in a casing or enclosure 20 of the electrical apparatus to be energized.

The electrical cable 16 includes a central or main conductor 22, insulation 24 disposed about conductor 22, and a conductive shield 26 disposed about insulation 24, which is grounded as indicated at 28.

The stationary portion of the connector 10 may be constructed in any suitable manner. For example, it maybe constructed as described in the hereinbefore mentioned copending application. In general, stationary member 14 includes an axially disposed electrical conductor 30, one end of which is adapted for connection to the encased electrical apparatus, and the other end of which is threadably engaged-with a terminal or contact member 32. Terminal 32 has a plurality of upmolded rubber, defines a tubular chamber 52 for receiving the fuse 50. The first and second electrical contacts 44 and 46 are disposed in spaced relation within chamber 52, with the first contact 44 being disposed at one end of the chamber and electrically connected to the conductor 22 of the shielded cable 16. The second electrical contact 46 is disposed near the other end of chamber 52, and is connected to terminal 48, which may be offset from the axis of the chamber 52 to provide an elbow typeplug-in connector. Terminal 48 depends from one end of a tapered chamber, defined by a shroud 54 of insulating material, which is complementary to the portion of insulating body member 36 of stationary member 14 which ex- Fuse 50, which may be a current limiting fuse-asdisclosed in the hereinbefore mentioned copendingapplication, has first and second electrodes or

ferrules

56 and 58, respectively, which are mounted on the endsof I an insulating body member 60, and which are electrically interconnected with a fusible element (not shown) which extends through an opening in the insulating body member 60. The fuse 50 is held in a circuit wardly extending, circumferentially spaced spring.

finger members 34, which are complementary to a terminal in the plug-in member 12. An insulating body member 36 surrounds the electrical conductor 30 and terminal 32, and a sleeve 38 of arc extinguishing material is disposed at the upper end of the fingers 34, for extinguishing an arc generated when the plug-in member 12 is removed from its cooperative circuit closing arrangement with the stationary member 14. A metallic flange member 39 may be embedded in the insulating body portion of the stationary member 14, which may be welded, or otherwise fastened to the easing 20 of the electrical apparatus.

Plug-in member 12 includes an insulating body porclosing arrangement between contacts 44 and 46 by the spring type fingers on contact 46, and a suitable spring arrangement (not shown) which urges electrode 56 of fuse 50 against electrical contact 44. Fuse 50, as illustrated, is connected to a plug-like member 62, which is mechanically linked with the fuse 50, and which closes the other end of the fuse chamber 52, when it is in assembled relation with the plug-in member 12. The plug-like member 62 has a handle '64 attached thereto which may be engaged with a hook stick for withdrawing the plug-like member 62 and fuse 50 when it is desired to interrupt the circuit or replace the fuse. It will be noted that the second contact member 46 is constructed to allow the fuse 50 to be advanced therethrough, to enable'it to assume the proper operating position when it is inserted into the fuse holder.

For purposes of operator safety, it is desirable. to maintain a grounded shield between the energized conductive portion of connector 10 and operating personnel. Thus, the outer layer 42 of the plug-in connector is formed of a conductive or semiconductive material, such as rubber filled with particulated carbon, or particulated silicon carbide, and it contacts the grounded shield 26.of the electrical cable 16, to continue the grounded shield of the cable about the connector. I

When the fusible element of fuse 50 melts to interrupt the circuit due to a fault on the load side of fuse 50, terminal 48, contact 46, and electrode 58 drop to zero potential, while conductor 22, contact 44 and electrode 56 remain at line potential. This causes the electrostatic field to change, sharply increasing the maximum voltage stress adjacent electrode 56 and conductor 44, which initiates corona discharges in the surrounding air. The corona attacks the inner annular wall of fuse chamber 52, causing erosion, burning, carbonizing, and tracking across this surface. FIG. 1 illustrates a solution to this problem, which does not require any major modification to the connector, or a substantial increase in its manufacturing cost. A coating 70 of stress grading'material is applied uniformly about the inner annular surface of chamber 52, starting at and preferably contacting the first electrical contact 44, and extending towards contact 46 for a distance sufficient to surround electrode 56 and to reduce the stress at the terminus of the coating to a level which will not initiate partial discharges or corona. Coating 70 may be a semiconductive paint, i.e., a paint having a predetermined voltage dependent resistivity which conducts current in direct response to themagnitude of the electrostatic stress adjacent thereto. If desired, a coating similar to coating 70 may be disposed adjacent to and contacting the second contact member 46 further imof connector shown in FIG. 1, constructed according to another embodiment of the invention, with like reference numerals indicating like components. In this embodiment, an annular resilient, insulating liner member 72 is disposed between the shield or coating 70 and the electrode 56 of the fuse 50, with its axial opening being sized to snugly accept the electrode 56,

and its length sufficient to enclose the end of coating 70 l which is remote from contact 44. In this embodiment,

The first electrical contact 44 is also a pencil-like contact, with thepo'rtion which makes electrical contact with portion 80 of electrode 56' being of substantially the same outside diameter as portion 80. This construction places the insulating body portion 60' of the fuse 50 between the major portion of electrode 56 and the inside wall of chamber 52, and also substantially increases the distance through the air between the electrode 56' and contact 44, and the wall of chamber 52, with both factors contributing to a lowering of the electrical stress at the wall of chamber 52. This embodiment 'may also be used in cooperation with the other embodiments disclosed herein. For example, a

resilient liner may be disposed between the fuse body 60 and the wall of chamber 52, a conductive or semiconductive coating-or shield may be disposed on have to beof an impractithe coating 70 may be a good electrical conductor,

such as an aluminum coating, it may be partially conductive, such as a coating containing particulated carbon, or' it may be semiconductive, i.e., having a predetermined voltage dependent characteristic, such as provided by silicon carbide coating formulations. In

any event, enclosure of the edge of coating 70 substantially reduces the length of coating which is required.

Also, instead of applying the coating 70 to the inside wall portion of chamber 52, as illustrated in the embodiment of FIG. 1, it would also be practical to make the coating or shield an integral part of the resilient liner 72.

FIG. 3 is a fragmentary view of the plug-in portion 12 of connector 10 shown in FIG. 1, constructed according to still another embodiment of the invention. Like reference numerals in FIGS. 3 and 1 indicate like components. In this embodiment of the invention, the construction of the fuse 50 is changed, as illustrated by fuse 50' in FIG. 3, whereby the fuse has an internal or recessed electrode56' disposed on at least the end which makes electrical contact with the electrical contact 44 and the electrical contact 44 is also modified, as illustrated at 44' in FIG. 3.

More specifically, the insulating body portion 60 of fuse 50 has its internal'diameter threaded at at least one of its ends, for-receiving and threadably engaging electrode 56, which has a threaded outside diameter,-

and a contact portion 80 which extends outwardly from the end of the fuse body for a short predetermined distance. The contact portion is much smaller in diame- 6 the inner wall asillustratedin FIG. 1, or between a resilient liner and the wall, as shown in FIG. .2, with the shield, or coating being connected to contact 44', i

desired. a In summary, there has been disclosed a new and improved fusible electrical connector for connecting a shielded electrical cable to a load circuit, with the connector. having load-make and load-break capabilities, and with the fuse limiting the powerdissipated at the contacts of the connector, in the event of a fault occurring in the load circuit. Further, when the fuse clears the circuit after a fault, the connector is protected from corona damage which occurs in prior art devices due to a change in the electrostatic field following a blowing of the fuse. This is accomplished by reducing the maximum electrical stress about the fuse electrode which is still at line potential, or about both fuse electrodes, by grading the stress, by excluding air from the highly stressed area, by enlarging the clearances between the electrode and wall of the fuse chamber, or by a combination of these constructions.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative, and not in a limiting sense.

We claim as our invention:

1. An electrical connector comprising:

a plug-in member adapted for connection to a shielded electrical conductor, said plug-in member including an insulating body portion, first electrical shielding means surrounding said insulating body portion adapted to contact the shield of the shielded electrical conductor, first and second electrical contacts and a terminal,

said insulating body portion defining a tubular chamber, with said first and second electrical contacts being disposed in spaced relation therein,

said first electrical contact being adapted for connection to the shielded electrical conductor,

said terminal being connected to said second electrical contact, and adapted to releasably engage a complementary terminal,

\ a fuse having an insulating body member, first and second electrodes, and a fusible element con nected between its first and second electrodes, said fuse being removably disposed within the chamber of said insulating body portion with its first and second electrodes in contact with said first and second electrical contacts respectively, and with its first and second electrodes spaced from the wall of the tubular chamber of said insulating body portion, second electrical shielding means disposed within the chamber of said plug-in member, in contact with the annular inner surface thereof, starting adjacent to said first electrical contact and extending .toward said second electrical contact for a predetermined distance, to surround and shield the first electrode of said fuse, said second electrical shielding means having a voltage dependent resistivity selected to prevent corona discharges from occurring between the first and second electrodes of said fuse when the fusible element melts and interrupts the circuit between the first and second electrodes, and a resilient liner member disposed within the chamber of the plug-in member, having an aperture sized to snugly but removably receive the fuse, anddisposed adjacent to the first electrical contact, between thev second shielding means and the fuse. 2. An electrical connector comprising: a plug-in member adapted for connection to a shielded electrical conductor, said plug-in member including an insulating body portion, first electrical shielding means surrounding said insulating body portion adapted to contact the shield of the shielded electrical conductor, first and second electrical contacts, and a terminal, said insulating body portion defining a tubular chamber, with said first and second electrical contacts being disposed in spaced relation therein, said first electrical contact being adapted for connection to the shielded electrical conductor,

said terminal being connected to said second electrical contact and adapted to to releasably engage a diameter smaller than the outside diameter of its insulating body member, with said first electrical contact having a diameter which is substantially the same as that of the first electrode, to provide a substantial clearance between the first electrode and first electrical contact, and the surrounding chamber defined by the insulating body portion of said plug-in member.

The electrical connector of i 3. claim 2 including second electrical shielding means disposed within the chamber of said plug-in member, in contact with the inner annular surface thereof, starting adjacent the first electrical contact and extending towards the second electrical contact for a predetermined dimension, to surround and shield the first electrode of the fuse.

4. The electrical connector of claim 2 wherein the second electrical shielding means has a predetermined volta e dependent resistivity.

5. %'he electrical connector of claim 2 wherein the second electrical shielding means is electrically connected to the first electrical contact.

6. The electrical connector of claim 2 including a resilient liner member disposed within the chamberof the plug-in member, adjacent the first electrical contact, between the insulating body member of the fuse and the second shielding means.

Claims

1. An electrical connector comprising: a plug-in member adapted for connection to a shielded electrical conductor, said plug-in member including an insulating body portion, first electrical shielding means surrounding said insulating body portion adapted to contact the shield of the shielded electrical conductor, first and second electrical contacts and a terminal, said insulating body portion defining a tubular chamber, with said first and second electrical contacts being disposed in spaced relation therein, said first electrical contact being adapted for connection to the shielded electrical conductor, said terminal being connected to said second electrical contact, and adapted to releasably engage a complementary terminal, a fuse having an insulating body member, first and second electrodes, and a fusible element connected between its first and second electrodes, said fuse being removably disposed within the chamber of said insulating body portion with its first and second electrodes in contact with said first and second electrical contacts respectively, and with its first and second electrodes spaced from the wall of the tubular chamber of said insulating body portion, second electrical shielding means disposed within the chamber of said plug-in member, in contact with the annular inner surface thereof, starting adjacent to said first electrical contact and extending toward said second electrical contact for a predetermined distance, to surround and shield the first electrode of said fuse, said second electrical shielding means having a voltage dependent resistivity selected to prevent corona discharges from occurring between the first and second electrodes of said fuse when the fusible element melts and interrupts the circuit between the first and second electrodes, and a resilient liner member disposed within the chamber of the plug-in member, having an aperture sized to snugly but removably receive the fuse, and disposed adjacent to the first electrical contact, between the second shielding means and the fuse.

2. An electrical connector comprising: a plug-in member adapted for connection to a shielded electrical conductor, said plug-in member including an insulating body portion, first electrical shielding means surrounding said insulating body portion adapted to contact the shield of the shielded electrical conductor, first and second electrical contacts, and a terminal, said insulating body portion defining a tubular chamber, with said first and second electrical contacts being disposed in spaced relation therein, said first electrical contact being adapted for connection to the shielded electrical conductor, said terminal being connected to said second electrical contact and adapted to to releasably engage a complementary terminal, and a fuse having an insulating body member and first and second electrodes, said fuse being disposed within the chamber of said plug-in member, with its first and second electrodes in contact with the first and second electrical contacts, respectively, the first electrical contact of said fuse having a diameter smaller than the outside diameter of its insulating body member, with said first electrical contact having a diameter which is substantially the same as that of the first electrode, to provide a substantial clearance between the first electrode and first electrical contact, and the surrounding chamber defined by the insulating body portion of said plug-in member.

3. The electrical connector of claim 2 including second electrical shielding means disposed within the chamber of said plug-in member, in contact with the inner annular surface thereof, starting adjacent the first electrical contact and extending towards the second electrical contact for a predetermined dimension, to surround and shield the first electrode of the fuse.

4. The electrical connector of claim 2 wherein the second electrical shielding means has a predetermined voltage dependent resIstivity.

5. The electrical connector of claim 2 wherein the second electrical shielding means is electrically connected to the first electrical contact.

6. The electrical connector of claim 2 including a resilient liner member disposed within the chamber of the plug-in member, adjacent the first electrical contact, between the insulating body member of the fuse and the second shielding means.