Separable electric connector module with gas-actuated piston

A separable connector module of the fault-actuated piston type comprises an aluminum container tube, a bore contact member within the container tube, and a piston for actuating the bore contact member in response to closing on a fault. The piston is primarily of copper but has a thin coating of dissimilar metal on its exterior. A sleeve of copper tightly fitting with the container tube acts as a cylinder for receiving the exterior of the piston in contacting relationship between copper and said dissimilar metal. The sleeve has adjacent one end an integrally formed end wall containing a central opening, and a copper-alloy nut is brazed to the end wall adjacent the central opening.

CROSS-REFERENCE TO RELATED PATENT 
The subject matter of this application is related to that of U.S. Pat. No. 
4,175,817--Tachick et al., assigned to the assignee of the present 
invention, which patent is incorporated by reference in the present 
application. 
BACKGROUND 
This invention relates to a separable electrical connector module and, more 
particularly, to a module of this type that includes a bore contact and 
coupled thereto a piston upon which gas generated during a fault-closing 
operation acts to drive the bore contact toward a mating rod contact, 
thereby to facilitate fault-closing. 
In typical prior art designs of such modules, the piston has been made of 
copper, and it is adapted to slide within a container tube that is made of 
aluminum. A body of electrical insulation is molded or cast about the 
container tube; and the aluminum of the container tube provides high 
strength, enabling the container tube to withstand the high pressures 
usually associated with such molding or casting. The use of aluminum for 
the container tube also provides excellent compatibility with the 
insulating material, particularly when the insulating material is an epoxy 
compound such as used for integrated bushings. Examples of processes that 
have been used for incorporating the insulation are injection molding, 
compression molding, pressure gelation molding, and liquid casting. 
Another feature of the above-described typical prior art design is that the 
aluminum container tube usually contains a thickened end wall that has a 
threaded opening therein for receiving an externally-threaded copper 
conductor. Electric current entering the module through the copper 
conductor follows a path that extends through the mating threads of the 
conductor and the container tube, into the aluminum container tube, and 
then into the copper piston to the bore contact. 
Because of oxide formation and the relatively high resistance of a bare 
aluminum-to-copper connection, it has been customary to tin-plate the 
aluminum container tube where it is to contact the threaded conductor and 
the piston. However, there have been a number of problems associated with 
this tin-plating. Tin-plating aluminum, especially a long tube with an end 
wall containing a threaded opening (such as the container tube), has 
proven to be difficult and expensive. It has been especially difficult to 
provide a good tin-plate coating on the threads of the opening. An 
excessive amount of plating on these threads interferes with proper 
mechanical mating of the conductor module and the threaded conductor, 
while the absence of adequate plating has led to electrical problems under 
high current or load-cycling conditions. 
The sliding connection between the piston and container tube has also had 
problems. When both the copper piston and the surrounding cylinder portion 
of the aluminum container tube are tin-plated, the sliding contact between 
piston and cylinder is one of tin on tin, which leads to high drag forces 
and material galling, both of which can result in undesirably slow 
piston-response during fault-closing operations. 
SUMMARY 
An object of our invention is to provide a separable connector module of 
the fault-actuated piston type in which the above-described tin-plated 
joints between copper and aluminum are eliminated, but the above-described 
advantageous features of the aluminum container tube are retained. 
Another object is to provide a design of the type set forth in the 
immediately-preceding paragraph which can be easily and inexpensively 
fabricated. 
In carrying out our invention in one form, we provide a separable connector 
module adapted to conduct current between a mating connector module and an 
externally-threaded bushing well stud. The first-mentioned module 
comprises an insulating housing having an elongated receiving passageway 
and a rigid container tube of aluminum closely fitted within said 
passageway. The container tube has one inner end located adjacent the 
bushing well stud. Intermediate the ends of the container tube are a bore 
contact member and a piston fixed thereto and adapted to drive the bore 
contact member along the axis of the container tube in response to gas 
being generated within the container tube. The piston is primarily of 
copper but has a thin coating of dissimilar metal on its exterior. A 
sleeve of copper tightly fitting within the container tube acts as a 
cylinder for slidably receiving the exterior of the piston in contacting 
relationship between copper and said dissimilar metal. The sleeve has 
adjacent the inner end of the container tube an integrally-formed end wall 
containing a central opening. Brazed to the end wall adjacent the central 
opening is a copper-alloy nut having internal threads adapted to mesh with 
threads on the bushing well stud.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
The separable connector shown in FIG. 1 is in many respects similar to that 
shown and claimed in the aforesaid Tachick et al. patent. Accordingly, the 
same reference numerals are used for the parts of FIG. 1 as are used for 
corresponding parts in the Tachick et al. patent; and reference may be had 
to the Tachick et al. patent for a detailed description of such parts. 
Generally speaking, where the parts have been fully described in the 
Tachick et al. patent, they will not be described in the present 
application except insofar as deemed necessary to provide an understanding 
of the present invention. Emphasis in the present description will be 
placed on those features that are not shown in the Tachick et al. patent. 
In the separable connector module 10 of FIG. 1, there is a container tube 
28 that is positioned within an elongated receiving passageway 14 in the 
insulating housing 12. In a preferred form of the invention, the bulk of 
the housing 12 is of organic insulation which is injection molded about 
the container tube. The container tube is of aluminum, and this aluminum 
imparts high strength to the container tube to enable it to effectively 
withstand the high pressures associated with such injection molding. The 
use of aluminum for the container tube also provides excellent 
compatibility with the surrounding insulating material, particularly when 
the insulating material is an epoxy compound such as used for integrated 
bushings. This compatibility eliminates the need for conformal coatings to 
provide matching coefficients of thermal expansion between the container 
tube material and the epoxy of the bushing. It is to be understood that 
the insulation can be incorporated by other suitable molding or casting 
processes, such as compression molding or pressure gelation molding. 
Tightly fitting within the container tube 28 is a sleeve 29 of copper. This 
sleeve 29 extends from the lower end of the container tube to a location 
just below a retaining ring 40 in the top half of the module. The sleeve 
29 has a cylindrical interior wall, or bore, 48 that has one or more 
keyribs formed in it. In the illustrated embodiment there are three 
keyribs, but in a commercial form of this invention only a single keyrib 
is used. Each keyrib has a substantially rectangular cross-section and 
runs longitudinally of the sleeve 29 from near its lower end 34 to its 
upper end. The illustrated keyribs are equally spaced about the axis of 
the container tube. 
The piston upon which gas pressure acts during a fault-closing operation is 
shown at 66a. This piston 66a is slidably received within the copper 
sleeve 29 in the container tube 28. At its upper end the piston 66a 
includes a cylindrical body portion 67 that contains in its outer 
periphery three angularly-spaced keyways that respectively receive the 
three angularly-spaced keyribs 50 on the bore of the surrounding copper 
sleeve 29, as is best shown in FIG. 4. 
The piston 66a has a downwardly-extending generally tubular portion that 
comprises three angularly spaced segments 102. As best shown in FIG. 3, 
these segments 102 are biased radially-outward into high pressure 
engagement with the bore of the copper sleeve 29, contacting this bore in 
angularly-spaced locations between the keyribs 50. The segments 102 are 
preferably integral with the body portion 67 of the piston 66a, and both 
the body portion and the segments are made of copper. The entire exterior 
of the copper piston is preferably plated with tin or some other suitable 
dissimilar metal such as nickel so as to minimize the formation on this 
exterior of copper oxides that could interfere with making a good 
electrical connection between the segments 102 and the surrounding sleeve 
29. 
The segments 102 are biased radially outward into high pressure engagement 
with the surrounding sleeve 29 by means of a split annular spring ring 
110. This spring ring 110 is located within the tube defined by segments 
102 and has resilience that tends to expand the ring in diameter. This 
resilience acts upon the surrounding segments 102 to force them radially 
outward into high pressure engagement with the surrounding copper sleeve 
29. A more detailed description of the annular split ring is contained in 
application Ser. No. 224,404--Goldbach, now U.S. Pat. No. 4,350,406 filed 
Jan. 12, 1981, and assigned to the assignee of the present invention, 
which application is incorporated by reference in the present application. 
Current flows through the module 10 via a path that extends upwardly from 
the bottom of the module through the copper sleeve 29 in the container 
tube 28 and then into segments 102 of the piston 66a via the contacting 
regions between segments 102 and sleeve 29 in the vicinity of spring ring 
110. The high pressure engagement between the segments 102 and the copper 
sleeve 29 in this region provides a good electrical connection between 
these parts. Although sufficient to provide for a good electrical 
connection, the engaging pressure is not sufficiently high to interfere 
with the desired upward movement of the piston under fault-close 
conditions, as is referred to hereinafter. 
Although the piston 66a of this module has been modified from that of the 
Tachick et al. patent, the general operation of the module is basically 
the same as that of the Tachick et al. patent. That is, an arc developed 
in the bore 60 of the snuffer liner 62 of ablative material during a 
fault-close operation generates gases which pass downwardly through the 
central port 69 in the bore contact 54 and quickly build up a pressure 
beneath piston 66a. This pressure acts to drive the piston upwardly along 
with the bore contact 54 coupled thereto, thereby facilitating closing 
under fault conditions. A spring-loaded check valve (such as 75 in the 
Tachick et al. patent) can be used in the port 69, but has been omitted in 
FIG. 1 to simplify the drawing. 
It is highly desirable that the piston move upwardly along the cylinder 
under fault-closing conditions with as little delay as possible. The 
arcing time, which it is desired to minimize, is directly proportional to 
this delay. In prior modules having tin-to-tin contact between piston and 
cylinder, a typical arcing time was 2.7 msecs under high fault current 
conditions; whereas with our module having the above-described 
copper-to-tin contact, we have consistently achieved arcing times in the 
neighborhood of 2.2 msecs under corresponding fault current conditions. 
The drag force in our module has typically measured about 20 pounds as 
compared to the 50 to 100 pounds typically present in the above-described 
prior module. 
Electric current is carried to and from the lower end of the connector 
module by means of a stationary bushing well stud 90, shown in FIG. 1 in 
dot-dash lines. This bushing well stud 90 is of copper and has an 
externally-threaded upper end. The connector module 10 includes a nut 92 
at its lower end having internal threads 94 that are adapted to mesh with 
the external threads of the bushing well stud 90 so that electric current 
can flow across the threaded connection between the nut 92 and the stud 
90. The copper sleeve 29 has an integral end wall 96 that contains a 
central opening 97. The upper end of the nut 92 is fitted within this 
central opening 97, and the nut is brazed to the end wall 96 at 98. 
The nut 92 is of a copper alloy which has good machinability and a 
relatively high strength so that the internal threads 94 machined into it 
are of high strength, which enables us to avoid stripping or other damage 
to the threads during installation of the module, when the module is 
tightly threaded onto the bushing well stud 90. The high strength of the 
threads also enables the module to be repeatedly removed and reinstalled 
on other bushing well studs without damage to the threads. 
A suitable material for the nut 92 is a brass containing, by weight, 60-63% 
copper, 2.5-3% lead, remainder zinc except for incidental impurities. 
Another suitable material is a heat-treatable leaded copper-nickel alloy 
containing, by weight, about 97.3% copper, 0.8-1.2% nickel, 0.8-1.2% lead, 
and miscellaneous incidental impurities. 
As pointed out in the introductory portion of this specification, it has 
been customary to make the container tube and its lower end wall with 
threaded opening of a single aluminum part, as in the aforesaid Tachick 
patent. This has necessitated plating this part with tin or the like, with 
special care being taken where current enters and leaves the container 
tube, i.e., at the threads and along the bore portion that receives piston 
66a. We are able to completely dispense with such plating because of the 
presence of copper sleeve 29 and the copper-alloy nut brazed to the 
internally-formed lower end portion 34 of sleeve 29. The presence of the 
copper-alloy nut makes it possible to make a good electrical connection 
with the externally threaded copper stud 90 without the need for tin plate 
between the threads on the nut and those on the stud. The presence of the 
copper sleeve 29 as a liner in the aluminum container tube 28 provides a 
tubular copper surface along which the tin-plated copper piston is able to 
slide, thus providing copper-to-tin contact between these parts, which 
obviated the need for tin plating on the surrounding cylinder in the 
region where there is sliding engagement. 
The copper sleeve 29 can be made from ordinary copper water pipe, with its 
integral end wall 96 being formed by a spinning and/or die forming 
operation. This copper water pipe is not readily machinable, but we 
obviate the need for machining this pipe because we utilize for the sleeve 
29 a simple configuration that can be developed without machining. The 
keyribs 50 in the sleeve 29 are formed with a die that deforms the 
cylindrical portion of the sleeve to form the keyribs. This deforming 
operation can be made simpler if only a single keyrib is used, which is 
the design that we use in a commercial embodiment. 
The copper sleeve 29 is incorporated into the aluminum container tube 28 by 
pressing the sleeve into a counterbored portion of the container tube and 
then spinning the free end of the container tube (which is at its lower 
end in FIG. 1) around the back side of wall 96 of the copper sleeve. This 
spinning operation forms on the free end of the container tube 28 a 
radially-inwardly projecting annular lip 95 that presses tightly against 
the back of wall 34, thus retaining the sleeve 29 in place within the 
counterbore of the container tube. 
The aluminum of the container tube 28 is readily machinable, and thus tube 
28 can easily be machined to provide any needed grooves, counterbores, or 
the like. 
In referring herein to "aluminum", we intend to comprehend within this term 
not only substantially pure aluminum but also aluminum-base alloys. 
Likewise the term "copper" is intended to comprehend copper-base alloys as 
well as substantially pure copper. 
While we have shown and described particular embodiments of our invention, 
it will be obvious to those skilled in the art that various changes and 
modifications may be made without departing from our invention in its 
broader aspects; and we, therefore, intend herein to cover all such 
changes and modifications as fall within the true spirit and scope of our 
invention.