Pressure-operated switch for a high-voltage interrupting module

An improved switch for a high-voltage device in which ignition of a power cartridge moves an insulative piston located in a conductive member away therefrom and into a passageway in an insulative liner. The piston moves a contact through the passageway and away from the conductive member to break an electrical interconnection between the conductive member and the movable contact, thereby opening the switch. The switch includes an insulative housing engageably surrounding, holding and fixing the relative positions of the conductive member and the liner. An interiorly relieved extension is formed at and about one end of the liner, and an exteriorly relieved region is formed in and about one end of the conductive member, whereby the region may be telescoped into and conformally engage the inside of the extension so that the conductive member and liner partially overlap along a tortuous interface so as to increase the interrupting capability of the switch by enhancing the isolation between the power cartridge and the passageway.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved pressure-operated switch for a 
high-voltage interrupting module. More specifically, the present invention 
relates to an improvement of the switches disclosed in commonly assigned 
U.S. Pat. Nos. 4,342,978 issued Aug. 3, 1982 in the name of Meister, and 
4,370,531 issued Jan. 25, 1983 in the name of Tobin, and in the following 
commonly assigned U.S. patent application: Ser. No. 179,367 filed Aug. 18, 
1980 (now abandoned in favor of continuation application Ser. No. 550,201, 
filed Nov. 9, 1983) in the name of Jarosz and Panas; Ser. No. 179,366 
filed Aug. 18, 1980 (now abandoned in favor of continuation application 
Ser. No. 539,396, filed Oct. 6, 1983) in the name of O'Leary, and Ser. No. 
437,925 which issued Jan. 24, 1984 as U.S. Pat. No. 4,427,963, and Ser. 
No. 437,926, both filed Nov. 1, 1982 in the names of Jarosz and Panas. 
2. Prior Art 
The above-noted commonly assigned patents relate to various aspects of a 
pressure-operated switch and to a high-voltage interrupting module 
containing the switch. The switch may include a pair of contacts which are 
normally electrically interconnected, for example, by direct abutment 
therebetween or, preferably, by interconnecting them with a shearable or 
tearable metallic disc or membrane. In preferred embodiments of the 
switch, one contact is stationary, while the other is movable, although 
both may be movable. The contacts are separable by relative movement along 
a fixed line of direction to open a gap therebetween, thereby opening the 
switch. One of the contacts, preferably the stationary contact, contains a 
bore which, in conjunction with a piston or trailer positioned between the 
movable contact and the bore, defines a closed chamber. The chamber houses 
a power cartridge or similar pressure-generating device. 
The switch may be in electrical shunt with a fuse, a fusible element which, 
as well as the switch, preferably reside within a common housing. When the 
switch is closed (i.e., when the contacts thereof are electrically 
interconnected), the resistance of the current path through the switch is 
much lower than resistance of the current path through the fusible 
element, and, accordingly, a majority of the current flowing through the 
module flows through the switch. Thus, the module has a very high 
continuous current rating. Upon opening the switch, the contacts separate 
and current is rapidly commutated from the switch to the fusible element 
where it is interrupted. Separation of the contacts is achieved by 
igniting the power cartridge, which evolves high pressure within the 
chamber. This high pressure acts against the piston and the forces 
produced thereby rapidly drive the piston and the movable contact away 
from the stationary contact, which shears the disc to break the normal 
electrical interconnection and open the switch. The power cartridge may be 
ignited in response to a trip signal produced by apparatus which senses a 
fault current or other overcurrent in a circuit in which the interrupting 
module is connected for protection thereof. Such trip-signal-producing 
apparatus may be that which is disclosed in commonly assigned U.S. patent 
application, Ser. Nos. 506,942; 506,943; and 506,944, all filed June 22, 
1983 in the name of Ruta. 
In specific embodiments of the switch described in the above patents and 
patent applications, a second stationary contact is included. When the 
switch is closed, the movable contact and the second stationary contact 
are electrically interconnected with a second shearable disc. When the 
power cartridge is ignited, movement of the movable contact also shears 
the second disc. As the movable contact moves away from the first 
stationary contact, it is telescoped into a bore formed in the second 
stationary contact. This bore may be lined with an insulative sleeve and 
the movable contact may be covered with an insulative sleeve, so that such 
telescoping results in the formation of a second gap between the movable 
contact and the second stationary contact. 
The movable contact moves rapidly away from the first stationary contact 
through a passageway in an insulative liner. The piston also enters the 
passageway in the liner to physically isolate the moving contact and the 
second stationary contact from the ignition products of the power 
cartridge. This isolation prevents or suppresses the formation of any arc 
between the separating contacts and between the stationary contacts. In 
preferred embodiments of the switch, the stationary contacts and the liner 
are engageably surrounded, and have their relative positions fixed, by an 
insulative housing, which maintains the stationary contacts and the liner 
end-to-end with the bores and the passageway axially aligned. 
Tests of earlier versions of the switch (such as those disclosed in the 
'978 and '531 patents and in the '367 and '366 applications) showed that, 
after the piston entered the liner, some of the ignition products of the 
power cartridge might, in some cases, flow along the liner-housing 
interface. Such flow, it was noted, might result in internal flashover of 
the open switch, i.e., undesired conduction there within. It is one object 
of the present invention to eliminate this problem. 
Additionally, it was noted that high electrical stress, which might also 
result in internal flashover of the open switch, could occur between the 
regions of abutment between the liner and the stationary contacts after 
the switch had opened. Another object of the present invention is the 
elimination of such flashover. 
SUMMARY OF THE INVENTION 
With the above and other objects in view, the present invention 
contemplates an improved switch for a high-voltage device. The switch 
improved by the present invention is generally of the type in which 
ignition of a power cartridge generates high pressure ignition products 
which move an insulative piston, which is normally located in a first bore 
formed in a conductive member or first stationary contact, away therefrom 
and into a passageway formed in an insulative liner. Such movement of the 
piston moves a movable contact through the passageway and away from the 
conductive member or first stationary contact to break an electrical 
interconnection between the conductive member or first stationary contact 
and the movable contact, thereby opening the switch. In specific 
embodiments, the switch improved by the present invention also includes a 
second stationary contact. In this case, movement of the movable contact 
away from the first stationary contact is accompanied by movement of the 
movable contact into a bore of the second stationary contact when the 
switch opens. The bore or bores in the passageway are aligned preferably 
by an insulative housing which engageably surrounds, holds and fixes the 
relative positions of the conductive member and the liner or of the 
stationary contacts and the liner in narrower embodiments. 
In the improved switch, an interiorly relieved extension is formed at or 
about one end of the liner and an exteriorly relieved region is formed in 
and about the outside of the conductive member or, in and about the 
stationary contacts where both are used. The relieved region is telescoped 
into and conformally engaged by the inside of the extension so that the 
conductive member or, where present, both stationary contacts and the 
liner partially overlap along a tortuous path. 
The amount of overlap between the conductive member or the stationary 
contacts and the liner is sufficiently long axially of the switch to 
concentrate the majority of the electrical stress which is present upon 
opening the switch within the liner. Further, the amount of overlap 
between the conductive member or both stationary contacts and the liner is 
sufficiently long axially of the switch to prevent the flow of the 
ignition products along the path made up of the tortuous interface between 
the extension and the relieved region and the interface between the liner 
and the housing. Moreover, the amount of overlap between the conductive 
member or both stationary contacts and the liner is sufficiently long 
axially of the switch to increase the total creepage distance along the 
path made up of the interface between the relieved region and the 
extension and the interface between the liner and the housing. This 
obviates flashover of the switch along this path. Lastly, the extension is 
preferably configured so that the ignition products which reach the 
interface between the relieved region of the conductive member or first 
stationary contact and the extension deform the extension outwardly 
against the housing in a lip-seal-like manner to prevent flow of such 
ignition products along the liner-housing interface.

DETAILED DESCRIPTION 
The present invention is used with an interrupting module 12. Because the 
module 12 is more completely described in the above U.S. patents and 
patent applications, it is only generally depicted in the drawing hereof 
and only generally described herein. 
Referring to FIG. 1, the module 12 includes a generally cylindrical 
open-ended insulative housing 14, which is closed by end plates 16. The 
housing 14 and the end plates 16 surround a fusible element 18 helically 
wound around a central axis of the housing 14 which may be embedded in a 
mass of a particulate fulgurite-forming medium, such as silica sand. The 
medium is in intimate engagement with the fusible element 18. The fusible 
element 18, which may be silver or copper, and the sand 20 interrupt fault 
currents or other overcurrents therethrough in a current-limiting or 
energy-limiting manner, according to well-known principles. The fusible 
element 18 may be similar to those disclosed in commonly assigned U.S. 
Pat. No. 4,359,708, issued Nov. 16, 1982 or U.S. patent application Ser. 
No. 437,776 filed Oct. 29, 1982, both in the names of Jarosz and Panas. 
The housing 14 also surrounds a switch 22 around which the fusible element 
18 may be maintained in its helical configuration by insulative supports 
23 such as those disclosed in commonly assigned U.S. patent application, 
Ser. No. 181,603, filed Aug. 27, 1980 in the names of Jarosz and Panas. 
The switch 22, which is improved by the present invention, may be generally 
constructed in accordance with the above U.S. patents and patent 
applications, and an example thereof is depicted in FIGS. 1 and 2. 
Specifically, the switch 22 includes a first conductive member 24, to 
which the left end plate 16 is attached and a second conductive member 26 
to which the right end plate 16 is attached. The first conductive member 
24 serves as a first stationary contact of the switch 22, while the second 
conductive member 26 serves as a second stationary contact of the switch 
22. The ends of the fusible element 18 may be rendered electrically 
continuous with the stationary contacts 24 and 26 by facilities 27 
described more fully in commonly assigned U.S. patent application Ser. No. 
439,444 filed Nov. 5, 1982 in the name of Jarosz. 
The switch 22 also includes a movable contact 28 (FIG. 2). Normally, the 
movable contact 28 is electrically continuous with both stationary 
contacts 24 and 26 so that a continuous low-resistance electrical path is 
formed between the member 24 and 26 via the movable contact 28. Because 
the resistance of this path is lower than the resistance of the fusible 
element 18, while the switch 22 is closed, as depicted in FIG. 2, the 
majority of the current flowing through the module 12 is normally shunted 
through the switch 22 and away from the fusible element 18. When the 
switch 22 opens, as described below, the current formerly flowing through 
the stationary contacts 24 and 26 and the movable contact 28 is commutated 
to the fusible element 18 for interruption. 
As shown in FIG. 2, the first stationary contact 24 has a central bore 30. 
At the left end of the central bore 30, a power cartridge 32, or other 
pressure-generating device, is located. The second stationary contact 26 
also contains a central bore 36. This bore 36 may be lined with an 
insulative sleeve 38. 
The movable contact 28 comprises a conductive member 40 surrounded by an 
insulative sleeve 42. The movable contact 28 is normally located between 
the stationary contacts 24 and 26 and within a passageway 44 formed 
through an insulative liner 46 between the stationary contacts 24 and 26. 
The stationary contacts 24 and 26, with the liner 46 therebetween, are held 
with the bores 30 and 36 and the passageway aligned by an insulative 
housing 48 which engageably surrounds the stationary contacts 24 and 26 
which are affixed thereto in a convenient manner. If desired, the 
stationary contacts 24 and 26 may be affixed to the housing 48 pursuant to 
commonly assigned and filed U.S. patent application Ser. No. 524,180, 
filed Aug. 17, 1983 in the names of Jackson and Scherer. As shown in FIG. 
1, the insulative support 23 may comprise a pair of notched fins 49, and 
the fusible element 18 may be helically maintained about the housing 48 by 
the fins 49, as described in commonly assigned U.S. patent application, 
Ser. No. 181,603 filed Aug. 27, 1980 in the names of Jarosz and Panas. As 
shown in FIG. 3, in earlier versions of the switch 22, the stationary 
contacts 24 and 26 and the liner 46 were cylindrical and were held in 
end-to-end abutment in the area denoted 49. 
With the movable contact 28 occupying the position shown in FIG. 2, the 
conductive member 40 thereof is electrically interconnected to the 
stationary contact 24 by a conductive shear disc 50 or other metallic 
diaphragm or member, which is shearable, tearable or the like. To the left 
of the diaphragm 50 is located an insulative piston or trailer 52. In the 
normal position of the movable contact 28 shown in FIG. 2, the piston 52 
normally occupies the bore 30 in the first stationary contact 24, and the 
movable contact 28 occupies the passageway 44 in the liner 46. 
The right end of the conductive member 40 is normally electrically 
interconnected to the second stationary contact 26 by a shear disc 54, 
which may be similar to the shear disc 50. The interior of the insulative 
sleeve 38 is sufficiently large to receive the conductive member 40 with 
its insulative sleeve 42 thereon. The passageway 44 of the liner 46 can 
receive both the conductive member 40 with the insulative sleeve 42 
thereon and the trailer 52. 
In the normal condition of the module 12, as shown in FIG. 2 and as 
previously described, the switch 22 carries a majority of the current 
flowing in a protected high-voltage circuit (not shown) to which the 
module 12 is connected. This current flows through the stationary contacts 
24 and 26, the discs 50 and 54, and the movable contact 28. Little current 
normally flows through the fusible element 18. Should a fault current or 
other overcurrent occur in the protected circuit (not shown) to which the 
module 12 is connected, apparatus (not shown) detects this condition and 
ignites the power cartridge 32. Ignition of the power cartridge 32 causes 
it to evolve large quantities of high-pressure gas which acts on the left 
end of the piston 52. The force applied to the piston 52 by the high 
pressure moves the piston 52 rightwardly and also moves rightwardly the 
movable contact 28 (i.e., the conductive member 40 with the insulative 
sleeve 42 thereon). Rightward movement of the piston 52 and of the movable 
contact 28 severs, rips or tears the discs 50 and 54, thereby breaking the 
electrical interconnection between the movable contact 28, on the one 
hand, and both stationary contacts 24 and 26, on the other hand. Two gaps 
are thereby opened by the switch 22. The first gap exists between the left 
end of the conductive member 40 and the right end of the first stationary 
contact 24, while the second gap exists between the right end of the 
conductive member 40 and the left end of the second stationary contact 26. 
Both gaps are electrically insulated. Specifically, the first gap is 
electrically insulated by the reception of the piston 52 within the 
passageway 44 in the liner 46. The second gap is electrically insulated by 
the reception of the insulative sleeve 42 within the bore 36 of the 
insulative sleeve 38. The reception of the piston 52 by the passageway 44 
in the liner 46 is also intended to isolate the movable contact 28 and the 
stationary contact 26 from the ignition products of the power cartridge 
32, which may contain electrically conductive, arc-promoting materials. 
When the switch 22 opens, the current previously flowing therethrough is 
commutated to the fusible element 18. The action of the fusible element 18 
and of the silica sand 20 ultimately extinguishes this current, as is well 
known. 
After numerous tests of earlier versions of the module 12, it was found 
that after the switch 22 opened, the ignition products of the power 
cartridge 32 might, in some cases, flow from the area of abutment 49 
between the liner 46 and the stationary contacts 24 and 26 along the 
interface between the liner 46 and the housing 48, notwithstanding a close 
fit between the two and the use of adhesives therebetween. Such flow can 
have the deleterious consequence of encouraging conduction (flashover) 
between the stationary contacts 24 and 26, i.e. an internal failure of the 
switch 22 as and after it opens. Further, with the switch 22 open, high 
electrical stress in the area 49 (FIG. 3) could, in some cases, result in 
flashover of the switch 22 between the liner 46 and the housing 48 even if 
no ignition product flow therebetween occurred. 
To alleviate both problems, the present invention contemplates that the 
stationary contacts 24 and 26 and the liner 46 should assume 
configurations other than those shown (per FIG. 3) in the above patents 
and patent applications. Specifically, the stationary contacts 24 and 26 
are exteriorly, annularly relieved as shown at 62 and the liner 46 is 
extended and internally, annularly relieved as at extension 64. The ID of 
the extensions 64 is the same as, or slightly smaller than, the OD of the 
relieved regions 62 so that the contacts 24 and 26 and the liner 46 may be 
telescoped together as shown in FIG. 2 and held in this relationship by 
the housing 48. Adhesive may be present at the interface of each relieved 
region 62 and its corresponding extension 64. 
The described telescoping of the relieved regions 62 and the extensions 64 
lengthens and renders tortuous the path any ignition products must follow 
in flowing along the contact-liner 24-46 interface, thereby restricting 
such flow. Further, the effective axial extensions 64 of the liner 46 
leftwardly along the stationary contact 24 have been found to reduce 
electrical stress at the area 49 by requiring such stress, when the switch 
22 is open, to be concentrated in the high dielectric strength material of 
the liner 46. This reduces the possibility of flashover across the 
contacts 24 and 26 of the open switch 22 via a path along the 
liner-housing interface 46-48. Additionally, the metal-to-metal path or 
creepage distance between the contacts 24 and 26 and along the 
liner-housing 46-58 interface of the open switch 22 is also increased in 
length--that is, to the length of the tortuous path to aid in the 
prevention of flashover along the liner-housing interface 46-48. Lastly, 
any ignition products which manage to reside at the interface between the 
extensions 64 and the relieved regions 62 tend to deform the extensions 64 
outwardly against the interior of the housing 48. This lip-seal-like 
action of the extensions 64 aids the flow-restricting function of the 
tortuous path along the interface 62-64. 
Similar structure may be included at the right of the liner 46 and at the 
left of the second stationary contact 26 to reduce electrical stress at 
the junction thereof and to further increase the creepage distance along 
the liner-housing 46-48 interface. 
The above structure may be used with the invention of commonly assigned and 
filed U.S. patent application Ser. Nos. 524,181 and 525,205, filed Aug. 
17, 1983 and Aug. 22, 1983, respectively in the name of Jackson and 
Swanson, respectively. These latter inventions would have the effect of 
minimizing the quantity of ignition products available for flowing along 
the interface 62-64. 
As set forth in '926 application, the bore 44 of the liner 46 may be 
relieved, undercut or diametrically increased in size, as shown at 76. 
This provides a relief cavity or volume 78. Should interruption of a fault 
current or other overcurrent by the fusible element 18 generate sufficient 
heat to cause undue expansion of the liner 46 or the piston 52, the relief 
cavity or volume 78 provides a space into which the material of these 
elements can expand. Such expansion into the relief cavity or volume 78 
prevents outward forces or pressure from being applied to the housing 14, 
to the end plates 16, and to the members 24 and 26, thus ensuring that the 
module 12 remains integral during and following operation thereof. 
With these advantages and features in mind, it should be apparent that 
various changes, alterations, and modifications may be made to the 
preferred embodiment of the present invention as described herein, without 
departing from the spirit and scope of the present invention as defined in 
the appended claims.