U.S. patent number 3,670,287 [Application Number 05/064,383] was granted by the patent office on 1972-06-13 for electrical connector assembly.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to August I. Keto.
United States Patent |
3,670,287 |
Keto |
June 13, 1972 |
ELECTRICAL CONNECTOR ASSEMBLY
Abstract
A load-break electrical connector assembly including a plug-in
cable connector having a probe which includes a first electrical
conductor, and a bushing assembly which includes a second conductor
adapted to engage the first conductor of the cable connector. A
magnetic clamp is disposed in the bushing assembly which prevents
removal of the cable connector from the bushing assembly when the
magnitude of current flowing through the first and second
electrical conductors exceeds a predetermined magnitude.
Inventors: |
Keto; August I. (Sharpsville,
PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22055570 |
Appl.
No.: |
05/064,383 |
Filed: |
August 17, 1970 |
Current U.S.
Class: |
439/39; 439/305;
439/186 |
Current CPC
Class: |
H01H
9/085 (20130101); H01H 1/54 (20130101); H01R
13/53 (20130101) |
Current International
Class: |
H01H
1/54 (20060101); H01H 1/00 (20060101); H01H
9/08 (20060101); H01H 9/00 (20060101); H01R
13/53 (20060101); H01r 011/30 () |
Field of
Search: |
;339/12,30,79,82,111,74,75,91 ;70/275 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Champion; Marvin A.
Assistant Examiner: Hafer; Robert A.
Claims
I claim as my invention:
1. An electrical connector assembly comprising:
a cable connector having a probe which includes a first electrical
contact,
a bushing assembly having a second electrical contact,
said cable connector and bushing assembly having complementary
surfaces, enabling said cable connector to be plugged into said
bushing assembly and form a sealed electrical connection between
said first and second electrical contacts,
and magnetically responsive protective means disposed in said
bushing assembly, having an aperture through which the probe of
said cable connector extends when said cable connector and bushing
assembly are coupled in an assembled relation,
the dimensions of the aperture in said protective means being
responsive to the magnitude of the current flowing through said
electrical connection, with the dimensions of the aperture being
reduced when the current exceeds a predetermined magnitude,
preventing de-coupling of said cable connector from said bushing
assembly.
2. The electrical connector assembly of claim 1 wherein the portion
of the probe which extends through and past the aperture in the
protective means increases in diameter to provide a shoulder which
cooperates with the protective means when its aperture has reduced
its dimensions, to prevent de-coupling of the cable connector from
the bushing assembly.
3. The electrical connector assembly of claim 2 wherein the
shoulder is formed in the first electrical conductor.
4. An electrical connector assembly comprising:
a cable connector having a probe which includes a first electrical
contact,
a bushing assembly having a second electrical contact,
said cable connector and bushing assembly having complementary
surfaces, enabling said cable connector to be plugged into said
bushing assembly and form a sealed electrical connection between
said first and second electrical contacts,
protective means disposed in said bushing assembly, having an
aperture through which the probe of said cable connector extends
when said cable connector and bushing assembly are coupled in an
assembled relation,
the portion of the probe which extends through and past the
aperture in the protective means increases in diameter to provide a
shoulder which cooperates with the protective means when its
aperture has reduced its dimensions, to prevent de-coupling of the
cable connector from the bushing assembly,
the dimensions of the aperture in said protective means being
responsive to the magnitude of the current flowing through said
electrical connection, with the dimensions of the aperture being
reduced when the current exceeds a predetermined magnitude,
preventing de-coupling of said cable connector from said bushing
assembly, and cooperative insulating rod and tube members disposed
to squeeze an arc formed between the first and second electrical
conductor means, with the insulating rod being part of the probe
assembly and fixed to the end of the first electrical conductor,
and the insulating tube member being disposed in the bushing
assembly.
5. The electrical connector assembly of claim 4 wherein the
shoulder is formed in the first electrical conductor.
6. The electrical connector assembly of claim 4 wherein the
shoulder is formed in the insulating rod member.
7. An electrical connector assembly comprising:
a cable connector having a probe which includes a first electrical
contact,
a bushing assembly having a second electrical contact,
said cable connector and bushing assembly having complementary
surfaces, enabling said cable connector to be plugged into said
bushing assembly and form a sealed electrical connection between
said first and second electrical contacts,
and protective means disposed in said bushing assembly, having an
aperture through which the probe of said cable connector extends
when said cable connector and bushing assembly are coupled in an
assembled relation,
the dimensions of the aperture in said protective means being
responsive to the magnitude of the current flowing through said
electrical connection, with the dimensions of the aperture being
reduced when the current exceeds a predetermined magnitude,
preventing de-coupling of said cable connector from said bushing
assembly, said protective means including at least two metallic
segments spaced by biasing means, which provide an aperture having
a predetermined diameter, with the mutual attraction of the
segments overcoming the biasing means at a predetermined current
flow, to reduce the spacing between the segments and the dimensions
of the aperture.
8. An electrical connector assembly, comprising:
a cable connector having a probe which includes a first electrical
contact,
a bushing assembly having an aperture with a second electrical
contact disposed therein,
said cable connector and bushing assembly having complementary
surfaces, enabling said cable connector to be plugged into said
bushing assembly and form a sealed electrical connection between
the first and second electrical contacts,
means for extinguishing an arc between the first and second
electrical contacts, including an insulating rod fixed to the end
of the first electrical contact, and an insulating tubular member
disposed at the entrance end of the aperture of said bushing
assembly, through which the probe passes in making and breaking the
electrical connection, and a metallic, magnetic clamp disposed
between the second electrical contact and said insulating tubular
member, having an aperture therein which accepts the probe of the
cable connector when it is plugged into the bushing assembly,
said magnetic clamp being responsive to the magnitude of current
flowing through the electrical connection, reducing the dimensions
of its aperture when a predetermined current magnitude is exceeded,
to prevent removal of the probe from said magnetic plant.
9. The electrical connector assembly of claim 8 wherein the portion
of the probe which extends past the aperture in the magnetic clamp
increases in diameter to provide a shoulder which cooperates with
the clamp when it reduces the dimension of its aperture, to prevent
withdrawal of the probe from the magnetic clamp.
10. The electrical connector assembly of claim 9 wherein the
shoulder is formed in the first electrical conductor.
11. The electrical connector assembly of claim 9 wherein the
shoulder is formed in the insulating rod member.
12. The electrical connector assembly of claim 8 including metallic
means interconnecting the magnetic clamp and the second electrical
contact, with the magnetic clamp providing arcing contacts for the
second electrical contact.
13. The electrical connector assembly of claim 8 wherein the
insulating tubular member includes a tubular extension on one end
thereof which extends into the aperture of the magnetic clamp, with
the magnetic clamp deforming the tubular extension to prevent
decoupling of the probe from the bushing assembly when the
predetermined current magnitude is exceeded.
14. The electrical connector assembly of claim 13 wherein the
tubular extension on the insulating tubular member defines at least
one longitudinal slot which starts at the end of the tubular
extension.
15. The electrical connector assembly of claim 14 including
metallic means interconnecting the magnetic clamp and the second
electrical contact, with the magnetic clamp providing an arcing
contact for the second electrical contact.
16. An electrical connector assembly, comprising: a plug-in cable
connector including insulating means defining a cavity, and having
a probe extending outwardly from the bottom of the cavity, said
probe including a first electrical conductor, and an insulating rod
formed of an arc extinguishing material fixed to the outwardly
extending end of said first electrical conductor,
a bushing assembly including an insulating body member having first
and second ends, an aperture which starts at its first end, a
second electrical contact disposed in the aperture with its end
facing the first end of the insulating body member, including a
pressure terminal adapted to engage the first electrical conductor
of said probe, and a tubular insulating member formed of arc
extinguishing material disposed in the aperture at the first end of
said insulating body member,
and magnetic clamp means disposed in the aperture of said
insulating body member, adjacent the pressure terminal of said
second electrical conductor, said magnetic clamp means including at
least two metallic segments which are spaced apart by biasing
means, and which overcome the biasing means to reduce the spacing,
and the dimensions of an aperture therethrough, when a
predetermined current magnitude through the first and second
electrical conductors is exceeded,
said probe having at least first and second different diameters,
with the first diameter being smaller than the second, providing a
shoulder between the two diameters which passes through the
aperture in the magnetic clamp means when the cable connector is
plugged into the bushing assembly, and with said magnetic clamp
means cooperating with said shoulder to prevent removal of the
probe from the magnetic clamp means when the magnetic clamp means
has reduced the dimensions of its aperture in response to current
flow.
17. The electrical connector assembly of claim 16 wherein the
shoulder in the probe is formed in the first electrical
conductor.
18. The electrical connector assembly of claim 16 wherein the
shoulder in the probe is formed in the insulating rod.
19. The electrical connector assembly of claim 16 wherein the
tubular insulating member includes a tubular extension which enters
the aperture in the magnetic clamp means.
20. The electrical connector assembly of claim 19 wherein the
tubular extension includes at least one longitudinal slot therein.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to electrical connector
assemblies, and more specifically to electrical connector
assemblies of the plug-in 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 enables 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
auxiliary load-break switches are acceptable functionally, they add
substantially to the cost of the underground distribution system
and thus plug-in type electrical connector assemblies were
developed which have load break capability. For example, copending
application Ser. No. 1,828, filed Jan. 9, 1970, which is assigned
to the same assignee as the present application, discloses a
plug-in electrical connector having load-break capabilities. 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 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 the 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 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 arc 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 by providing
the plug-in cable connector and bushing with cooperative insulating
sleeve and rod members, 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 arc 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.
Most load-break electrical connector assemblies in use today are
manually operated by an operator with a hot stick, as they are
relatively simple in construction, low in cost, and they perform
very reliably. The simple operating requirement of sliding the
plug-in cable connector into the bushing assembly completes the
electrical circuit between the probe contact of the cable connector
and the pressure type contact of the bushing assembly, and the
reverse operation breaks the circuit. The necessary clearances are
provided to promote the smooth and effortless operation. However,
on fault close-in, the effortless close-in operation may be
defeated, as internal pressures are created which may "blow-back"
the cable connector, and defeat the intended operation. The
smoother and easier the close-in, the more likely blow-back will
occur on a fault close-in.
It would be desirable to provide a new and improved manually
operable load-break electrical connector assembly which eliminates
the blow-back problem associated with such connectors of the prior
art when they are closed on a fault. Further, it would be desirable
to provide a connector assembly having this non-blowback feature,
while still providing the smooth, effortless operation associated
with prior art load-break electrical connectors.
SUMMARY OF THE INVENTION
Briefly, the present invention is a new and improved circuit
interrupter of the plug-in electrical connector type, having a
plug-in 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.
Blow-back of the plug-in connector on fault close-in is eliminated
by protective means which includes an automatically operated
magnetic clamp disposed in the bushing assembly, which is actuated
when the magnitude of the current flowing through the bushing
exceeds a predetermined value, such as full load current plus a
reasonable overload. The magnetic clamp, when actuated, reduces the
dimensions of its aperture, preventing withdrawal of the probe
contact on the plug-in cable connector from the bushing
assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better understood, and further advantages and
uses thereof more readily apparent, when considered in view of the
following detailed description of exemplary embodiments, taken with
the accompanying drawings, in which:
FIG. 1 is an elevational view, partially in section, of an
electrical connector assembly constructed according to a first
embodiment of the invention;
FIG. 2 is a perspective view of the quench tube and magnetic clamp
used in the electrical connector assembly shown in FIG. 1;
FIG. 3 is an elevational view, partially in section, of an
electrical connector assembly constructed according to another
embodiment of the invention;
FIG. 4 is a perspective view of the quench tube and magnetic clamp
used in the electrical connector assembly shown in FIG. 3; and
FIG. 5 is an elevational view, partially in section, of an
electrical connector assembly constructed according to still
another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and FIG. 1 in particular, there is
shown 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 which have first and second conductor means
between which an electrical arc is formed, with arc confining and
extinguishing means disposed to confine and extinguish the arc.
More specifically, connector assembly 10 includes a first portion
including a plug-in cable connector 12, and a second portion
including a bushing assembly 14, which when assembled provide a
sealed electrical connection. The plug-in cable connector 12 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 12 includes a hood portion 16 and a main body
portion 22, both formed of 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 assembly 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 the shielded electrical cable (not shown)
within the main body portion 22 of the cable connector 12, and its
other end is part of the probe assembly 23 which extends coaxially
into cavity 18. The probe assembly 23 also includes an insulating
rod member 24, called the snuffer rod, which is secured to the
lower end of conductor 20. Conductor 20 has first and second
diameters 25 and 27, respectively, which provide a shoulder 29 at
their junction, for purposes which will be hereinafter explained.
The second diameter 27 is larger than the first, and it starts at
the outwardly extending end of conductor 20. Conductor 20 and
snuffer rod 24 have the same diameters at their junction, providing
a smooth transition from the insulating rod 24 to the conductor 20.
The snuffer rod 24 is formed of an arc extinguishing material, with
methyl methacrylate filled with glass fibers being an excellent
material, as disclosed in my copending application Ser. No. 1,827
filed Jan. 9, 1970, which is assigned to the same assignee as the
present application, but other arc extinguishing materials may be
used if desired. The lower end 26 of snuffer rod 24 may be curved
or rounded to facilitate its introduction into the bushing assembly
14. Conductor 20 may join the conductor of the shielded cable at a
90.degree. 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 a 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 assembly.
The bushing assembly 14 includes a cylindrical elongated insulating
body member 28 which is preferably formed of a rigid solid
insulating system, a conductive sleeve or tubular member 30, a
terminal stud 32, a replaceable contact member 34, an insulating
sleeve member 36, commonly called the quench tube, which is formed
of arc confining and extinguishing material and which may be the
same material of which the snuffer rod 24 is formed, and a metallic
mounting ring assembly 38.
The body member 28 has first and second ends 40 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
coefficient 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 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.sub.2 O.sub.3.sup. .
3H.sub.2 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 copper,
with the tube having first and second ends 45 and 46, respectively,
and an aperture 48. The aperture 48 has a uniform diameter except
for a shoulder or step 50 which reduces the diameter of the
aperture for a short longitudinal dimension at a predetermined
location intermediate the first and second ends 45 and 46,
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 30 and extending to the location
of shoulder 50. 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 or 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 48 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 30, and also hermetically seals end 46 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 FIG. 1, conductive sleeve member 30 is sealingly
disposed in the aperture 44 of body member 28, with its first end
45 starting within the aperture 44 a predetermined dimension from
the first end 40 of body member 28, and with its second end 46
being substantially aligned with the second end 42 of body member
28.
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 64, which, along with the flange portion 60,
extend toward the first end 40 of the body member 28, and which
have openings for receiving clips disposed on the cable termination
to mechanically secure the cable connector in assembled relation
with the bushing 14.
The embedded flange 60 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 14 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 the casing 68. The
mounting ring member 38 may then be welded to the casing 68, as
illustrated by the welding bead 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 the portion 58 of mounting member 38, and the casing 68,
and the bushing 14 secured in place by a conventional spring and
flange assembly (not shown), disposed on the encased end of bushing
14. 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
coefficient of thermal expansion of the mounting ring member 38 and
body member 28, a coating 70 of resilient material may be disposed
on the flange 38. For example, as disclosed in U.S. Pat. No.
3,504,106, which is assigned to the same assignee as the present
application, the coating 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 the 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 ensure that an oil seal has been
obtained between the conductive sleeve members 30 and body member
28.
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 terminal portion 84 and conductive sleeve
members 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 30 and rotated, using a tool designed
for this purpose, until the end of the threaded portion is turned
tightly against shoulder 50, to provide a 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. The outside diameter of
pressure terminal portion 84 is reduced near its extreme end, and a
spring member 86 is provided 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 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 a 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. If
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 91, such as sprayed aluminum, may be disposed about the
body member 28, starting between the shoulder 80 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. Quench tube member 36 has a threaded portion 96 which
cooperates with the internal threads 52 of conductive sleeve member
30. Adjacent the first end 45 of conductive sleeve member 30, 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 to limit the inward travel of quench
tube 36 and properly locate its inner end 92. 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 the plug-in connector 12.
A sealant and lubricant, such as silicone grease, should be used to
insert quench tube 36 into cooperative engagement with conductive
sleeve member 30, to seal the small clearances between the quench
tube 36 and the adjacent inner wall of the insulating body member
28. This will prevent an arc from following this path to the outer
surface of bushing member 14, where it may proceed to ground.
In the operation of the electrical connector 10, the plug-in cable
connector 12 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 at which connector 10 is
associated, or in its connected load, ionized gas is produced by
the resulting arc between the conductors of connector 12 and
bushing assembly 14, which tends to blow-back the connector 12,
defeating the closure attempt. The force of the blow-back is
reduced by chamber 102, disposed between contact 34 and terminal
32, but it would be desirable to completely eliminate the
possibility of blow-back. Chamber 102 is defined by the inside wall
of conductive sleeve member 30, starting at the lower end of
contact member 34 and terminating at end 103, a predetermined
distance from the lower end of contact member 34. Excess volume in
conductive 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 provides space for ionized gases to expand,
cool and condense. 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 a live
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.
When the plug-in cable connector 12 is decoupled from the bushing
assembly 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 84 and
terminal 20 of plug-in connector 12, with the arc 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 an arc
drawn in a 7,200 volt circuit in which a load current of 200
amperes is flowing is extinguished within one-half to one cycle. In
the 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. In the prior art, the end 90 of the
quench tube 36 is disposed immediately adjacent the upper end of
the pressure terminal 84, but in the embodiment of the invention
shown in FIG. 1, end 90 of the quench tube 36 is spaced from the
pressure terminal 84, for reasons which will be hereinafter
disclosed.
If there is a low impedance fault in the load upon closing or
coupling the cable connector 12 with the bushing assembly 14,
protective current limiting means, such as fuses or breakers in the
high voltage cable feeders, will clear the circuit and limit the
maximum current to the fault close-in rating of the electrical
connector, such as 10,000 amperes in a 7,200 volt circuit. The
10,000 ampere fault current, however, may develop a back pressure,
due to heat and ionized gases, which is sufficient to overcome the
closing force applied by the operator with the hot stick, blowing
back the connector with possible hazard to the operating personnel.
This invention precludes such an occurrence by providing protective
means which is automatically brought into operation by the flow of
fault current, to clamp the probe 23 and prevent its withdrawal
from the bushing assembly 14.
FIG. 1 illustrates protective means 110, which, as illustrated more
clearly in the perspective view of FIG. 2, includes first and
second metallic segments 112 and 114. Segments 112 and 114 are
formed of a magnetic material having a high permeability and a low
retentivity, such as soft iron. Segments 112 and 114 are each
substantially semi-circular in general cross-section, and they are
disposed in bushing assembly 14 between the pressure terminal 84
and the quench tube 36, such that they form a tubular, cylindrical
electromagnet about conductor 20 when connector 12 is plugged into
bushing assembly 14, with conductor 20 functioning as a one turn
coil and segments 112 and 114 as the iron core of an electromagnet,
very similar to an electromagnet of the horseshoe type.
The flat faces of one segment are aligned with similar faces on the
other segment. For example, the flat faces 116 and 118 on segment
114, are aligned with the flat faces on segment 112, but the
aligned faces are spaced therefrom by a predetermined dimension
120. When spaced by this dimension, the segments 112 and 114 define
an aperture 122 which has substantially the same diameter as the
aperture through the quench tube 36, as illustrated in FIG. 2, with
the end 92 of the quench tube being in contact with the upper ends
of the two segments or very close thereto, not exceeding about
0.020 inch.
The spacing 120 between the segments 112 and 114 is maintained by
suitable biasing or resilient means disposed between their adjacent
aligned faces, such as indicated generally at 124 and 126.
Resilient means 124 and 126 may be small coil springs, or any other
suitable resilient spacing means may be used, such as small leaf
springs.
The outer surfaces of segments 112 and 114 are threaded, such as
with threads 128 on segment 112, enabling the resulting protective
assembly 110 to be properly positioned in bushing assembly 14 by
turning it into the tubular conductive sleeve member 30, after the
contact member 34 has been threadably inserted into conductive
means 30. The threads on the outer surfaces of these segments also
enable these segments to be removed and replaced, during any
required maintenance procedures. The lower end of protective
assembly 110 is spaced from the pressure terminal 84, with the
spacing not being critical, such as about 0.020 inch.
The two diameters 25 and 27 of the probe 23, the longitudinal
length dimension of the protective assembly 110, the
cross-sectional area of the flat surfaces or poles of the segments,
and the spacing 120 between the adjacent poles or faces of the
segments 112 and 114, are selected such that when the current
flowing through conductor 20 exceeds a predetermined magnitude, the
force of the resilient means, such as means 124 and 126, in
maintaining the spacing 120 between the segments 112 and 114 is
overcome by the mutual attraction of the segments 112 and 114. The
dimensions of the aperture 122 through protective means 110 are
changed when gap 120 is reduced, providing a dimension across
aperture 122, in a direction perpendicular to the faces of the
segments which is less than the diameter 27 of the probe 23. The
electromagnet or protective assembly 110 has a threshold, similar
to the pick-up point of an electromagnetic relay, with the
threshold, by design, being greater than the normal current rating
of the electrical connector 10, such as 200 amperes in a 7,200 volt
circuit, plus a predetermined overload. Beyond the current rating
plus overload, the protective assembly 110 will be actuated to
prevent withdrawal of the probe 23. The desired threshold value may
be obtained by properly selecting the gap dimension 120 and area of
the poles, with the attractive force between the segments when
saturated, being directly proportional to the first power of the
pole area, directly proportional to the current magnitude, and
inversely proportional to the air gap dimension or spacing between
the poles.
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, the electromagnetic or protective means
110, and the arc confining and extinguishing tubular sleeve member
36, are all replaceable.
In the operation of the electrical connector 10 shown in FIG. 1,
the operator, using a hot stick, plugs connector 12 into bushing 14
with a force which firmly seats connector 12 in assembled relation
with the bushing assembly 14. If there is a fault in the connected
load, the resultant arcing between the contacts upon closure may
produce pressures which attempt to blow-back the connector 12.
However, pressures of this magnitude will only be produced by
currents of sufficient value to actuate protective means 110.
Protective means 110 reduces the dimensions of its aperture 120,
preventing withdrawal of the probe 23 when the shoulder 29 of the
probe strikes the protective means 110.
In addition to preventing blow-back of connector 12, protective
means 110 also provides the additional function of protecting the
pressure terminal 84 from damage due to arcing. It will be observed
that similar to contact 34, the protective means 110 is in metallic
contact with the conductive sleeve member 30. Thus, protective
means 110 functions as arcing contacts for the main contact 34.
Upon insertion of the probe, arcing occurs between conductor 20 of
the probe and the protective means 110, with very little arcing
occurring when conductor 20 engages contact 34, as contact 34 is
effectively connected in parallel with the protective means 110.
Similarly, upon breaking the electrical circuit, very little arcing
occurs between conductor 20 and contact 34, as the current is
transferred to the protective means 110, with the major arcing
occurring as conductor 20 leaves protective means 110. Since
protective means 110 performs the function of arcing contacts, a
coating or insert of arc resistant material, such as insert 130,
may be disposed at the end of protective means 110 which is
adjacent end 92 of the quench tube 36. Suitable arc resisting
materials for example are electrically conductive alloys containing
tungsten.
The resilient or biasing means for spacing the segments 112 and 114
of the protective means 110, instead of being metallic spring
members, may be a thin wall extension of the quench tube 36, about
which the protective means 110 is disposed. This embodiment of the
invention is shown in FIGS. 3 and 4, with like reference numerals
in FIGS. 1, 2, 3 and 4 indicating like components, and like
reference numerals with a prime mark indicating like functions but
modified structures.
More specifically, FIG. 3 is an elevational view, in section, of an
electrical connector assembly 10' having a cable connector 12, as
hereinbefore described relative to FIG. 1, and a bushing assembly
14', similar to bushing assembly 14 in FIG. 1 except for having a
new quench tube 36' and a new protective means 110'. FIG. 4 is a
perspective view of quench tube 36' and protective means 110'.
Quench tube 36' is similar to quench tube 36, hereinbefore
described, except modified to include a thin walled extension 136,
best shown in FIG. 4. Extension 136 has an aperture which is an
integral continuation of the aperture in the main body portion of
the quench tube.
The length dimension of extension 136 is substantially the same as
the longitudinal length dimension of the protective means 110, and
its wall thickness is selected such that it will deform when
squeezed by the protective means 110'.
The protective means 110' includes first and second segments 112'
and 114', which are similar to segments 112 and 114 shown in FIG.
1, except having an aperture 122' when assembled which accepts the
outer diameter of the extension 136 on the quench tube 136', which
automatically sets and provides the desired predetermined air gap
120' between the aligned faces or poles of the segments 112' and
114'.
In this embodiment, additional biasing or resilient means are not
required between the poles of the segments, since they are spaced
apart by the extension 136 on the quench tube 36'. However,
alignment means, such as means 142 and 144, may be provided between
the segments to hold them in assembled relation while they are
being advanced into the desired longitudinal position within the
conductive sleeve or tubular member 30.
In the operation of the electrical connector assembly 10', if the
connector 12 is assembled with the bushing assembly 14' when there
is a low impedance fault in the load circuit, the segments 112' and
114' will be attracted to one another and close the gap 120'
between the poles, squeezing the extension 136 from opposite sides,
to deform the extension and cause it to prevent the removal of the
probe 23. This is unlike the embodiment of FIG. 1, wherein the
protective means itself contacted the shoulder 29 to block the
removal of the probe. Also, in this embodiment of the invention,
the protective means being lined with the extension 136, does not
function as arcing contacts for the contact member 34. An arc is
drawn between pressure terminal 84 of contact 34 and conductor 20,
which is immediately squeezed between the snuffer rod 24 and the
extension 136 on the quench tube 36'.
In order to facilitate the flexing or deformation of the extension
136 of the quench tube 36', under the urging influence of the
electromagnet or protective means 110', a plurality of longitudinal
slots, such as slots 148 and 150, may be disposed in the extension
136, starting at the extreme end 152 of the extension and extending
for a predetermined distance toward the main body portion of the
quench tube, such as about one-half the overall length of the
extension.
The longitudinal slots, such as slots 148 and 150 in addition to
adding mechanical flexibility to the extension, also promote the
extinction of an arc drawn between conductor 20 and contact 34. The
slots allow the segments 112' and 114' to function as arcing
contacts, as the current flow in the arc transfers from the contact
34 to the segments of the electromagnetic clamping means upon
withdrawal of the connector 12 from the bushing 14'. Also, the
current flow in the arc is broken into as many paths as there are
slots. Thus, the slots break up the arc into a plurality of
smaller, lower energy arcs, cooling the arcs and making it easier
to extinguish them as they are drawn through the slots in the arc
extinguishing material, and eventually squeezed between the
non-slotted portion of the extension 136 and the snuffer rod 24 on
the end of the probe 23.
While the embodiments of the invention hereinbefore disclosed have
illustrated the "step" or shoulder 29 in the probe 23 as being in
the electrically conductive portion of the probe, the step or
shoulder may also be disposed in the snuffer rod, if desired. FIG.
5 illustrates this embodiment of the invention, with like reference
numerals in FIGS. 3 and 5 indicating like components, and like
reference numerals with a double prime mark indicating like
functions with modified structures.
More specifically, FIG. 5 illustrates an electrical connector 10"
having a bushing assembly 14" similar to bushing assembly 14 of
FIG. 3, except with a modified contact 34", and with a connector
12" similar to connector 12 of FIG. 3, except with a modified probe
23".
Probe 23" is modified to step outwardly from the first or smaller
diameter 25 to the larger diameter 27 in the snuffer rod 24",
instead of in the electrical conductor 20". Thus, conductor 20" has
substantially the same diameter 25 throughout its length within the
cavity 18 of the connector 12", and pressure terminal 84" is
modified to make electrical contact with this smaller diameter of
contact 20", while being sufficiently flexible to pass the larger
diameter 27 of the snuffer rod 24". Thus, the shoulder 29" on the
snuffer rod 24" is caught and held by the protective means 110'.
When the protective means 110 is actuated by fault current, to
prevent the removal of the probe when it is attempted to be blown
back by the gas pressure produced within the connector assembly 10"
by fault current flow.
In summary, there has been disclosed new and improved electrical
connector assemblies of the plug-in, load-break type, which
automatically prevent blow-back of the cable connector on fault
closure, by utilizing a magnetic clamp disposed to prevent removal
of the cable conductor from the bushing when a predetermined
current magnitude is exceeded. The magnetic clamp may be provided
at a low cost, it is easily replaced if damaged, and it functions
automatically when there is danger of blow-back.
In addition to providing the blow-back protective function, the
magnetic clamp also functions, in certain embodiments, as arcing
contacts, which prevent damage to the main bushing contact, and in
other embodiments, in combination with a slotted extension on the
quench tube, it functions to break up the arc into a plurality of
smaller lower energy arcs, promoting quick extinction of the arc
with a minimum erosion of the arc extinguishing material, and with
lower pressures due to less heat and a smaller volume of ionized
gases.
* * * * *