U.S. patent number RE42,319 [Application Number 11/601,617] was granted by the patent office on 2011-05-03 for circuit protection device.
This patent grant is currently assigned to MERSEN France SB SAS. Invention is credited to Kenneth R. Martenson, Jerry L. Mosesian.
United States Patent |
RE42,319 |
Martenson , et al. |
May 3, 2011 |
Circuit protection device
Abstract
A voltage suppression device for suppressing voltage surges in
an electrical circuit, comprised of a voltage sensitive element
having a predetermined voltage rating, the voltage sensitive
element increasing in temperature as voltage applied across the
voltage sensitive element exceeds the voltage rating. Terminals are
provided for electrically connecting the voltage sensitive element
between a power line of an electrical circuit and a ground or
neutral line of the electrical circuit. A normally closed, thermal
switch is electrically connected in series with the voltage
sensitive element between the power line and the voltage sensitive
element, the thermal switch being thermally coupled to the voltage
sensitive element wherein the thermal switch moves from a normally
closed position to an open position to form a gap between the
thermal switch and the voltage sensitive element when the
temperature of the voltage sensitive element reaches a level
indicating an over-voltage condition. A non-conductive barrier that
is operable to move into the gap when the thermal switch moves to
an open position, the barrier preventing line voltage surges from
arcing between the thermal switch and the voltage sensitive
element.
Inventors: |
Martenson; Kenneth R. (Newbury,
MA), Mosesian; Jerry L. (Newburyport, MA) |
Assignee: |
MERSEN France SB SAS (Saint
Bonnet de Mure, FR)
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Family
ID: |
23483427 |
Appl.
No.: |
11/601,617 |
Filed: |
November 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09093367 |
Jun 8, 1998 |
6040971 |
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Reissue of: |
09376035 |
Aug 17, 1999 |
6430019 |
Aug 6, 2002 |
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Current U.S.
Class: |
361/124; 361/103;
361/127; 218/117; 361/118 |
Current CPC
Class: |
H01T
1/14 (20130101); H01T 1/12 (20130101); H02H
9/042 (20130101); H01C 7/126 (20130101); H01H
37/761 (20130101); H01H 9/32 (20130101) |
Current International
Class: |
H02H
1/00 (20060101); H02H 5/04 (20060101); H01H
9/32 (20060101) |
Field of
Search: |
;361/124,2,40,56,102-103,111,126-127,117-118,3-7,134-135
;218/117,89 ;337/273,278,110,282 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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42 41 311 |
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Jun 1994 |
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DE |
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0 716 493 |
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Jun 1996 |
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EP |
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03-073501 |
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Mar 1991 |
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JP |
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06-311643 |
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Nov 1994 |
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JP |
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11-133084 |
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May 1999 |
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JP |
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Other References
Harris Semiconductor, "Transient Voltage Supression Devices"
Transient V-I Characteristics Curves, p. 4-57, (Jun. 8, 1995).
cited by other.
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Primary Examiner: Fureman; Jared J.
Assistant Examiner: Bauer; Scott
Attorney, Agent or Firm: Kusner & Jaffe
Parent Case Text
This application is a continuation-in-part of application Ser. No.
09/093,367, filed on Jun. 8, 1998, now U.S. Pat. No. 6,040,971.
Claims
Having described the invention, the following is claimed:
1. A disposable voltage suppression device for suppressing voltage
surges in an electrical circuit, said device comprised of: a
voltage sensitive element having a first surface and a second
surface and a predetermined voltage rating across said first and
second surfaces, said voltage sensitive element increasing in
temperature as voltage applied across said first and second
surfaces exceeds said voltage rating; a first terminal having one
end electrically connected to said first surface of said voltage
sensitive element and another end connectable to a ground or
neutral line of an electrical circuit; a thermal element
electrically connected to said second surface of said voltage
sensitive element, said thermal element being an electrically
conductive solid at room temperature and having a predetermined
softening temperature; a second terminal having one end in
electrical connection with said second surface of said voltage
sensitive element and another end connectable to an electrical
power line of an electrical circuit, said voltage sensitive element
sensing the voltage drop between said electrical power line and
ground or neutral line, said second terminal being maintained in
electrical contact with said voltage sensitive element by said
thermal element and being biased away therefrom, wherein said
second terminal moves away from electrical contact with said
voltage sensitive element and breaks said electrical current path
if an over-voltage condition sensed by said voltage sensitive
element exceeds the voltage rating of said voltage sensitive
element and causes said voltage sensitive element to heat said
thermal element beyond its softening point; an arc shield movable
from a first position wherein said arc shield allows contact
between said second terminal and said voltage sensitive element to
a second position wherein said shield is disposed between said
second terminal and said voltage sensitive element when said second
terminal moves from electrical contact with said voltage sensitive
element; .[.and.]. a housing enclosing said voltage sensitive
element, said one ends of said first and second terminals, said
thermal element and said arc shield.Iadd.; and a wall contained
within the housing for separating the voltage sensitive element
from the arc shield over a substantial portion of the length of the
arc shield.Iaddend..
2. A voltage suppression device as defined in claim 1, wherein said
voltage sensitive element is a metal oxide varistor (MOV).Iadd.;
and the arc shield is movable along the wall that separates it from
the voltage sensitive element.Iaddend..
3. A voltage suppression device as defined in claim 2, wherein said
metal oxide varistor (MOV) is rectangular in shape.
4. A voltage suppression device as defined in claim 1, wherein said
thermal element is a metal solder comprised of a fusible
alloy.Iadd.; and the arc shield moves along the wall and passes
through at least a portion of a gap that is formed when said one of
said terminals moves out of contact with the voltage sensitive
element.Iaddend..
5. A voltage suppression device as defined in claim 4, wherein said
metal solder has a melting point of about 95.degree. C.
6. A voltage suppression device as defined in claim 1, wherein said
thermal element is an electrically conductive polymer.
7. A voltage suppression device as defined in claim 1, wherein
.[.said.]. .Iadd.the wall has an opening that is aligned with the
thermal element, and the .Iaddend.arc shield is supported in
.[.said.]. .Iadd.a .Iaddend.first position .[.by.]. .Iadd.to
provide access to said thermal element for passage of .Iaddend.said
second terminal.
8. A voltage suppression device as defined in claim 1, further
comprising a third terminal having one end in electrical connection
with said second surface of said voltage sensitive element and
another end connectable to an indicator device for indicating
whether said second terminal is in electrical connection with said
thermal element.
9. A voltage suppression device as defined in claim 8, wherein said
indicator device is a light emitting device.
10. A voltage suppression device as defined in claim 8, wherein
said indicator device is mounted to said housing.
11. A voltage suppression device as defined in claim 1, wherein
said arc shield is biased toward said second position .Iadd.and it
moves along a path that is substantially parallel to the
wall.Iaddend..
12. A voltage suppression device as defined in claim 11, wherein
said arc shield is biased by gravity.
13. A voltage suppression device as defined in claim 11, wherein
said arc shield is biased by a spring element.
14. A voltage suppression device as defined in claim 13, wherein
said arc shield is maintained in said first position by said second
terminal when said second terminal is in contact with said thermal
element.
15. A voltage suppression device as defined in claim 1, further
comprising indication means for indicating the condition of said
voltage suppression device.
16. A voltage suppression device as defined in claim 15, wherein
said indication means is an electrical switch.
17. A voltage suppression device as defined in claim 15, wherein
said indication means is a mechanical indicator.
18. A voltage suppression device for suppressing voltage surges in
an electrical circuit, said device comprised of: a voltage
sensitive element having a predetermined voltage rating, said
voltage sensitive element increasing in temperature as voltage
applied across said voltage sensitive element exceeds said voltage
rating; terminals for electrically connecting said voltage
sensitive element between a power line of an electrical circuit and
a ground or neutral line of said electrical circuit; a normally
closed, thermal switch comprised of one end of one of said
terminals, a surface of said voltage sensitive element and a
thermal element, said one end of one of said terminals being
maintained in electrical contact with said surface of said voltage
sensitive element by said thermal element, said thermal switch
being electrically connected in series with said voltage sensitive
element between said power line and said voltage sensitive element,
said thermal switch being thermally coupled to said voltage
sensitive element wherein said one of said terminals moves from a
normally closed position wherein said one of said terminals is
maintained in electrical contact with said surface of said voltage
sensitive element to an open position wherein said one of said
terminals moves out of electrical contact with said surface of said
voltage sensitive element to form a gap between said one of said
terminals and said voltage sensitive element when the temperature
of said voltage sensitive element reaches a level causing said
thermal element to melt; .Iadd.said one of said terminals including
a contact portion and a second portion that extends away from the
contact portion;.Iaddend. a non-conductive barrier operable to move
into said gap when said one of said terminals moves to an open
position, said barrier preventing line voltage surges from arcing
between said one of said terminals and said voltage sensitive
element.Iadd., the second portion of said one of said terminals
extends over at least a portion of the non-conductive barrier and
bends toward the thermal element so that the contact portion is
held by the thermal element until said thermal element begins to
melt, and said non-conductive barrier being biased toward the
thermal element, but being constrained from movement toward the
thermal element by contact with the second portion of said one of
said terminals at a location that is spaced away from the contact
portion, until said thermal element begins to melt.Iaddend..
19. A voltage suppression device as defined in claim 18, wherein
said voltage sensitive element is a metal oxide varistor
(MOV).Iadd., said voltage suppression device further including: a
housing having walls, a top member and a base member, connected to
one another to form an enclosure; a partition within said enclosure
separating a first portion of the enclosure from a second portion
thereof; the voltage sensitive element being located in the first
portion of the enclosure; an opening in the partition providing
access to said thermal element on the voltage sensitive element for
the passage of one of said terminals; the non-conductive barrier
being located in the second portion of the enclosure adjacent the
partition; and said non-conductive barrier operating to move along
the partition to pass into said gap so as to intercept an arc in
the gap between the voltage sensitive element and said one of said
terminals.Iaddend..
20. A voltage suppression device as defined in .[.claim 18, further
comprising an indicator device for indicating the condition of said
voltage suppression device.]. .Iadd.claim 19, wherein the
non-conductive barrier is a generally flat plate that is located
along a path that is generally parallel to the partition that
separates the first portion of the enclosure from the second
portion of the enclosure; and the second portion of said one of
said terminals is located along a path that intercepts the path of
the non-conductive barrier.Iaddend..
21. A voltage suppression device as defined in claim 20, wherein
.[.said indicator device is actuated by movement of said barrier.].
.Iadd.the non-conductive barrier is located between the partition
and said one of said terminals before passing into the gap between
said one of said terminals and said voltage sensitive
element.Iaddend..
22. A voltage suppression device as defined in claim 21, wherein
.[.said indicator device is an electrical switch.]. .Iadd.the
partition has an opening adjacent the thermal element, the
non-conductive barrier has an opening at least a portion of which
is in line with the opening in the partition.Iaddend..
23. A voltage suppression device as defined in claim 21, wherein
.[.said indicator device is a mechanical device.]. .Iadd.said one
of said terminals passes along the non-conductive barrier and bends
toward the thermal element to pass through the opening in the
partition, to connect to the thermal element.Iaddend..
24. A voltage suppression device as defined in claim 18, wherein
said thermal switch is comprised of a contact element held in
electrical contact with said voltage sensitive element by .[.a.].
.Iadd.said .Iaddend.thermal element, said contact element being
biased away from said voltage sensitive element.
25. A voltage suppression device as defined in claim 24, wherein
said thermal element is a low melting temperature solder
material.
26. A voltage suppression device as defined in claim 18, further
comprising a detachable base section attachable to said ground or
neutral line and said power line of said electrical circuit, said
voltage suppression device being received by said base section with
said terminals connecting said voltage sensitive element between
said power line of said electrical circuit and said ground or
neutral line of said electrical circuit.
27. A voltage suppression device as defined in claim 26, wherein
said voltage suppression device is received by said base section in
snap-lock fashion.
28. A voltage suppression device as defined in .[.claim 26, wherein
said voltage suppression device and said base section include
matching identification markings.]. .Iadd.claim 18, wherein the
non-conductive barrier is in a stationary state adjacent the
partition before the thermal element softens and, when the thermal
element softens, the non-conductive barrier passes along the
partition to the location of the thermal element to intercept an
arc that exists between said voltage sensitive element and said one
of said terminals.Iaddend..
29. A voltage suppression device for suppressing voltage surges in
an electrical circuit, said device comprised of: a voltage
sensitive element having a first surface and a second surface and a
predetermined voltage rating across said first and second surfaces,
said voltage sensitive element increasing in temperature as voltage
applied across said first and second surfaces exceeds said voltage
rating; a first terminal having one end electrically connected to
said first surface of said voltage sensitive element and another
end connectable to a ground or neutral line of an electrical
circuit; a thermal element electrically connected to said second
surface of said voltage sensitive element, said thermal element
being an electrically conductive solid at room temperature and
having a predetermined softening temperature; a second terminal
formed of a spring metal having one end in electrical connection
with said second surface of said voltage sensitive element and
another end connectable to an electrical power line of an
electrical circuit, said voltage sensitive element sensing the
voltage drop between said electrical power line and ground or
neutral line, said second terminal being bent from a normal and
relaxed configuration maintained in contact with said voltage
sensitive element by said thermal element, said second terminal
being inherently biased away from said voltage sensitive element
toward said normal and relaxed configuration, wherein said second
terminal springs away from electrical contact with said voltage
sensitive element and breaks said electrical current path if an
over-voltage condition sensed by said voltage sensitive element
exceeds the voltage rating of said voltage sensitive element and
causes said voltage sensitive element to heat said thermal element
beyond its softening point; an arc shield movable from a first
position wherein said arc shield allows contact between said second
terminal and said voltage sensitive element to a second position
wherein said .Iadd.arc .Iaddend.shield is disposed between said
second terminal and said voltage sensitive element when said second
terminal moves from electrical contact with said voltage sensitive
element; .[.and.]. .Iadd.the second terminal having a contact
portion for making electrical contact with the thermal element and
a second portion, the second portion extending through the path of
the arc shield and blocking the movement of the arc shield until
the thermal element reaches its softening point; and.Iaddend. a
housing enclosing said voltage sensitive element, .[.said one
ends.]. .Iadd.one end of each .Iaddend.of said first and second
terminals, said thermal element and said arc shield.
30. A voltage suppression device as defined in claim 29, wherein
said arc shield includes an indicator portion that provides a
visual indication external to said housing of movement of said arc
shield.
.Iadd.31. A disposable voltage suppression device as in claim 1,
wherein said second terminal has a contact portion and a second
portion that extends away from the contact portion, at least the
second portion of said second terminal being flexible and being
located over at least a portion of the arc shield and being bent
into a bent condition toward the thermal element, said contact
portion of said second terminal being held in electrical contact
with the voltage sensitive element by the thermal element before
the thermal element softens, said second terminal flexing outward
away from the thermal element when the thermal element softens, and
the arc shield being biased toward the thermal element before the
thermal element softens, but being constrained from movement toward
the thermal element by the second portion of said second terminal
at a location along the second portion that is spaced away from the
contact portion, until the thermal element softens and said second
terminal flexes outward away from the thermal element..Iaddend.
.Iadd.32. A disposable voltage suppression device as in claim 31.,
wherein said second terminal is released from said bent condition
and it flexes outward to a more straightened condition, when the
thermal element softens..Iaddend.
.Iadd.33. A disposable voltage suppression device as in claim 31,
wherein the second terminal flexes outward to a position spaced
from the thermal element when the thermal element softens, and at
least a portion of the arc shield passes between the thermal
element and said second terminal when the voltage across the
voltage sensitive element exceeds the voltage rating of the voltage
sensitive element and heats up the voltage sensitive element so as
to soften the thermal element..Iaddend.
.Iadd.34. A disposable voltage suppression device as in claim 1,
wherein in the normal a operation of the voltage sensitive element
the thermal element is solid, but when the voltage across the
voltage sensitive element increases beyond the voltage rating of
the voltage sensitive element, the voltage sensitive element heats
up to a temperature at or above said predetermined softening
temperature and the increased heat causes the thermal element to
soften, said second terminal has a contact portion and a second
portion that extends away from the contact portion, the contact
portion of said second terminal is held in electrical contact with
the voltage sensitive element solely by the thermal element and the
second portion of said second terminal is positioned to block the
path of the arc shield prior to the time that the thermal element
softens, and the contact portion of the second terminal is released
from the thermal element when the thermal element softens, and the
second terminal moves away from the thermal element, when the
thermal element softens, and releases the arc shield to pass along
a path in close proximity to the thermal element..Iaddend.
.Iadd.35. A disposable voltage suppression device as in claim 1,
wherein said second terminal has a contact portion and a second
portion, said contact portion being held in electrical contact with
the voltage sensitive element by the thermal element, and being
biased away from the voltage sensitive element by internal
mechanical forces in said second terminal, said arc shield is
located between the voltage sensitive element and the second
portion of said second terminal while the contact portion of said
second terminal is held by the thermal element, the second portion
of said second terminal extending through the path of the arc
shield to constrain the movement of the arc shield prior to the
softening of the thermal element, and said arc shield traversing a
path substantially parallel to the voltage sensitive element once
the thermal element softens and releases the contact portion of
said second terminal..Iaddend.
.Iadd.36. A voltage suppression device as in claim 18, wherein at
least the second portion of said one of said terminals is flexible
and is located over at least a portion of the non-conductive
barrier and is bent toward the thermal element, said contact
portion of said one of said terminals is held in electrical contact
with the voltage sensitive element by the thermal element before
the thermal element softens, said second portion of said one of
said terminals flexes outwardly away from the thermal element when
the thermal element softens, and the non-conductive barrier is
biased toward the thermal element before the thermal element
softens, but is constrained from movement toward the thermal
element by the second portion of said one of said terminals at a
location along the second portion that is spaced away from the
contact portion, until said one of said terminals flexes outward
away from the thermal element..Iaddend.
.Iadd.37. A voltage suppression device as in claim 18, wherein said
one of said terminals is flexible and, when released from said
thermal element, it flexes outward away from said thermal element
to a more straightened condition..Iaddend.
.Iadd.38. A voltage suppression device as in claim 18, wherein said
non-conductive barrier is positioned with its forward edge in close
proximity to the second portion of said one of said terminals, said
second portion of said one of said terminals is positioned to block
the path of the non-conductive barrier prior to the softening of
the thermal element..Iaddend.
.Iadd.39. A voltage suppression device as in claim 18, wherein said
thermal element is formed of an electrically conductive solder,
said second portion of said one of said terminals being biased away
from the thermal element by its internal mechanical forces, but its
contact portion is held in electrical contact with the voltage
sensitive element by the thermal element, said second portion of
said one of said terminals extends over at least a portion of the
non-conductive barrier and the second portion bends toward the
thermal element while the contact portion is held by the thermal
element, the non-conductive barrier is biased toward the thermal
element, but is constrained from movement toward the thermal
element by a region along the length of said second portion of said
one of said terminals, spaced away from the contact portion, while
the contact portion of said one of said terminals is held by the
thermal element..Iaddend.
.Iadd.40. A voltage suppression device as in claim 39, further
including: a molded plastic housing for retaining the voltage
sensitive element, at least two cavities formed in the housing, the
cavities being generally cylindrical, at least two springs, one
extending along the length of each of the cavities, the springs
biasing the non-conductive barrier toward the thermal element along
a path that is substantially parallel to the voltage sensitive
element, but the movement of the non-conductive barrier being
constrained by the second portion of said one of said terminals,
and the springs advancing the non-conductive barrier toward the
thermal element when the thermal element softens and the contact
portion of said one of said terminals moves away from the thermal
element..Iaddend.
.Iadd.41. A voltage suppression device as in claim 40, further
including at least one slot along the length of the molded plastic
housing, and at least one extension from the non-conductive barrier
that extends into the slot in order to guide movement of the
non-conductive barrier when the thermal element
softens..Iaddend.
.Iadd.42. A modular voltage suppression device for suppressing
voltage surges in an electrical circuit, said device comprised of:
a housing made of molded plastic having two side walls, two end
walls, a top and an open end; a base member made of molded plastic
forming a base that covers the open end of the housing; a voltage
sensitive element having a predetermined voltage rating, said
voltage sensitive element increasing in temperature as voltage
applied across said voltage sensitive element exceeds said voltage
rating; a compartment supported by the base member and located in
the housing for holding the voltage sensitive element; terminals
for electrically connecting said voltage sensitive element between
a power line of an electrical circuit and a ground or neutral line
of said electrical circuit; a normally closed thermal switch
comprised of one end of one of said terminals, a surface of said
voltage sensitive element and a thermal element, said one end of
one of said terminals being maintained in electrical contact with
said surface of said voltage sensitive element by said thermal
element, said thermal switch being electrically connected in series
with said voltage sensitive element between said power line and
said voltage sensitive element, said thermal switch being thermally
coupled to said voltage sensitive element wherein said one of said
terminals moves from a normally closed position wherein said one of
said terminals is maintained in electrical contact with said
surface of said voltage sensitive element to an open position
wherein said one of said terminals moves out of electrical contact
with said surface of said voltage sensitive element to form a gap
between said one of said terminals and said voltage sensitive
element when the temperature of said voltage sensitive element
reaches a level causing said thermal element to melt; a
non-conductive barrier operable to move into said gap when said one
of said terminals moves to an open position, said barrier
preventing line voltage surges from arcing between said one of said
terminals and said voltage sensitive element; each of said
terminals including a plug-in portion that extends from the bottom
surface of said base member for plugging in the voltage suppression
device and removing it from its plug-in condition; and the
compartment being supported by the base member and including a wall
for separating the voltage sensitive element from the
non-conductive barrier over a substantial portion of the length of
the barrier..Iaddend.
.Iadd.43. A voltage suppressor device as defined in claim 42,
further including: columnar channels along the wall that separates
the voltage sensitive element from the non-conductive barrier; the
non-conductive barrier being movable along the wall that separates
the voltage sensitive element from the non-conductive
barrier..Iaddend.
.Iadd.44. A voltage suppressor device as defined in claim 43,
further including: a plurality of springs in alignment with a
portion of the non-conductive barrier, at least one of said springs
being located in each of the channels; the springs causing the
non-conductive barrier to pass along the gap between said one of
said terminals and said voltage sensitive element when the thermal
element melts..Iaddend.
.Iadd.45. A voltage suppressor device as defined in claim 42,
wherein said wall extends adjacent one surface of the voltage
sensitive element, an aperture in said wall provides access to the
thermal element, said one of said terminals passes over a portion
of the barrier and extends through said aperture to contact the
thermal element before said one of said terminals moves out of
electrical contact with the voltage sensitive element; and the
non-conductive barrier moves along the wall and passes through at
least a portion of the gap when said one of said terminals moves
out of contact with the voltage sensitive element..Iaddend.
.Iadd.46. A voltage suppressor device as defined in claim 45,
wherein: the non-conductive barrier moves along the wall and passes
into the gap, between said one of said terminals and said voltage
sensitive element, when said one of said terminals moves out of
contact with the voltage sensitive element..Iaddend.
.Iadd.47. A modular voltage suppression device for suppressing
voltage surges in an electrical circuit, said device comprised of:
a housing having surrounding surfaces including walls, a top and a
base, all being joined together to form an enclosure; a compartment
wall within the enclosure; a voltage sensitive element having a
predetermined voltage rating, said voltage sensitive element
increasing in temperature as voltage applied across said voltage
sensitive element exceeds said voltage rating; the wall in the
enclosure supported by at least one of said surfaces of the
enclosure; the voltage sensitive element being located within the
enclosure; terminals for electrically connecting said voltage
sensitive element between a power line of an electrical circuit and
a ground or neutral line of said circuit; a normally closed thermal
switch comprised of one end of one of said terminals, a surface of
said voltage sensitive element and a thermal element; said one end
of one of said terminals being maintained in electrical contact
with said surface of said voltage sensitive element by said thermal
element; said thermal switch being electrically connected in series
with said voltage sensitive element and between said power line and
said voltage sensitive element, said thermal switch being thermally
coupled to said voltage sensitive element, wherein said one of said
terminals moves from a normally closed position wherein said one of
said terminals is maintained in electrical contact with said
surface of said voltage sensitive element to an open position
wherein said one of said terminals moves out of electrical contact
with said surface of said voltage sensitive element to form a gap
between said one of said terminals and said voltage sensitive
element, when the temperature of said voltage sensitive element
reaches a level causing said thermal element to melt; a
non-conductive barrier being urged to move toward said gap and
being operable to move into said gap when said one of said
terminals moves to an open position, said barrier preventing line
voltage surges from arcing between said one of said terminals said
voltage sensitive element; the non-conductive barrier being located
in a first position where it is stationary and located adjacent the
compartment wall, and being movable generally parallel to the
compartment wall to the location of the gap; and the compartment
wall being supported from at least one of the surfaces of the
enclosure and separating the voltage sensitive element from the
non-conductive barrier over a substantial portion of the length of
the barrier at least when the non-conductive barrier is in its
first position..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates generally to circuit protection
devices, and more particularly to a device that suppresses
transient current/voltage surges.
BACKGROUND OF THE INVENTION
Many of today's highly sensitive electronic components, such as
computer and computer-related equipment, that are used in
commercial and residential applications contain transient voltage
surge suppression (TVSS) devices. These devices protect sensitive
and/or expensive electronic circuits and components from damage
from over-voltage fault conditions. Such transient voltage surge
suppression systems are typically designed for moderate fault
conditions expected in normal use. In this respect, such systems
are designed to suppress relatively minor fault conditions, but are
not designed to protect against major over-voltage conditions.
Examples of major over-voltage conditions include those that may
occur from losing the system neutral or ground termination, or from
repetitive current pulses as from lightning strikes. Such major
over-voltage conditions can have catastrophic effects on sensitive
electronic circuits and components. To prevent such fault
conditions from reaching and damaging electronic circuits,
components and equipment, it has been known to utilize larger
voltage surge suppression devices. These devices are typically
deployed at a building's incoming electrical service power lines,
or within a building's power distribution grid to control power
surges in the electrical lines to the building, or in the
electrical lines to specific floors of the building. Such voltage
surge suppression devices typically include a plurality of
metal-oxide varistors (MOVs) connected in parallel between a
service power line and a ground or neutral line, or between a
neutral line and a ground line.
MOVs are non-linear, electronic devices made of ceramic-like
materials comprising zinc-oxide grains and a complex amorphous
inner granular material. Over a wide range of current, the voltage
remains within a narrow band commonly called the varistor voltage.
A log-log plot of the instantaneous voltage in volts versus the
instantaneous current in amps yields a nearly horizontal line. It
is this unique current-voltage characteristic that makes MOVs ideal
devices for protection of sensitive electronic circuits against
electrical surges, over-voltages, faults or shorts.
When exposed to voltages exceeding their voltage value, MOVs become
highly conductive devices that absorb and dissipate the energy
related to the overvoltage and simultaneously limit dump current to
a neutral line or ground plane. If an over-voltage condition is not
discontinued, the MOVs will continue to overheat and can ultimately
fail catastrophically, i.e., rupture or explode. Such catastrophic
failure may destroy the sensitive electronic equipment and
components in the vicinity of the MOVs. The destruction of
electrical equipment or components in the electrical distribution
system can disrupt power to buildings or floors for prolonged
periods of time until such components are replaced or repaired.
Moreover, the failure of the MOVs in a surge suppression system may
allow the fault condition to reach the sensitive electronic
equipment the system was designed to protect.
In U.S. Pat. No. 6,040,971 to Martenson et al., entitled CIRCUIT
PROTECTION DEVICE, there is disclosed a voltage suppression device
for protecting an array of metal oxide varistors in a surge
suppression system. The device was operable to drop offline an
entire array of MOVs in the event that a voltage surge reached a
level wherein one or more of the MOVs in the array might
catastrophically fail. In the disclosed device and system, a
trigger MOV was designed to have a lower voltage rating than any of
the MOVs in the array. Thus, the entire array would drop offline in
the event that a surge condition exceeded the voltage rating of the
trigger MOV. In some instances, however, it may be desirable to
maintain the array of MOVs active and to drop offline only those
MOVs sensing a voltage surge exceeding the voltage rating of that
particular MOV.
The present invention provides a circuit protection device, and a
transient voltage surge suppression system incorporating such
device, to protect an electrical system from catastrophic failure
due to excessive over-voltage conditions or repetitive fault
conditions.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a
voltage suppression device for suppressing voltage surges in an
electrical circuit. The device is comprised of a voltage sensitive
element having a first surface and a second surface and a
predetermined voltage rating across the first and second surfaces.
The voltage sensitive element increases in temperature as the
voltage applied across the first and second surfaces exceeds the
voltage rating. A first terminal has one end electrically connected
to the first surface of the voltage sensitive element and the other
end of the terminal is connected to a ground or neutral line of an
electrical circuit. A thermal element is electrically connected to
the second surface of the voltage sensitive element, the thermal
element being an electrically conductive solid at room temperature
and having a predetermined softening temperature. A second terminal
has one end in electrical connection with the second surface of the
thermal element and another end connected to an electrical power
line of an electrical circuit. The voltage sensitive element senses
the voltage drop between the electrical power line and ground or
neutral line. The second terminal is maintained in contact with the
thermal element by the thermal element and is biased away
therefrom. The second terminal moves away from electrical contact
with the thermal element and breaks the electrical current path if
an over-voltage condition sensed by the voltage sensitive element
exceeds the voltage rating of the voltage sensitive element. Such
an over-voltage causes the voltage sensitive element to heat the
thermal element beyond its softening point. An arc shield moves
from a first position wherein the arc shield allows contact between
the second terminal and the thermal element to a second position
wherein the shield is disposed between the second contact and the
thermal element, i.e., when the second terminal moves from
electrical contact with the thermal element.
In accordance with another aspect of the present invention, there
is provided a voltage suppression device for suppressing voltage
surges in an electrical circuit. The device is comprised of a
voltage sensitive element having a predetermined voltage rating.
The voltage sensitive element increases in temperature as voltage
applied across the voltage sensitive element exceeds the voltage
rating. Terminals electrically connect the voltage sensitive
element between a power line of an electrical circuit and a ground
or neutral line of the electrical circuit. A normally closed,
thermal switch is electrically connected in series with the voltage
sensitive element between the power line and the voltage sensitive
element. The thermal switch is thermally coupled to the voltage
sensitive element wherein the thermal switch moves from a normally
closed position to an open position to form a gap between the
thermal switch and the voltage sensitive element when the
temperature of the voltage sensitive element reaches a level
indicating an over-voltage condition. A non-conductive barrier is
operable to move into the gap when the thermal switch moves to an
open position. The barrier prevents line voltage surges from arcing
between the thermal switch and the voltage sensitive element.
It is an object of the present invention to provide a circuit
protection device to protect sensitive circuit components and
systems from current and voltage surges.
It is another object of the present invention to provide a circuit
protection device as described above to prevent catastrophic
failure of a transient voltage surge suppression (TVSS) system
within a circuit that may occur from repetitive circuit faults or
from a single fault of excessive proportion.
A further object of the present invention is to provide a circuit
protection device as described above that includes a current
suppression device and a voltage suppression device.
Another object of the present invention is to provide a circuit
protection device as described above for protecting a transient
voltage surge suppression system having metal-oxide varistors
(MOVs).
A still further object of the present invention is to provide a
circuit protection device as described above that includes a
metal-oxide varistor as a circuit-breaking device.
A still further object of the present invention is to provide a
circuit protection device as described above that is modular in
design and easily replaceable in a circuit.
These and other objects and advantages will become apparent from
the following description of a preferred embodiment of the present
invention taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take physical form in certain parts and
arrangement of parts, a preferred embodiment of which will be
described in detail in the specification and illustrated in the
accompanying drawings which form a part hereof, and wherein:
FIG. 1 is an exploded, pictorial view of a circuit protection
device illustrating a preferred embodiment of the present
invention;
FIG. 2 is a cross-sectional, side view of the circuit protection
device shown in FIG. 1 showing the device in a normal operating
configuration;
FIG. 3 is a cross-sectional, side view of the circuit protection
device shown in FIG. 1 showing the device after actuation by a
fault condition;
FIG. 4 is a partially sectioned, top-plan of the circuit protection
device shown in FIG. 1;
FIG. 5 is a partially sectioned, front elevational view of the
circuit protection device shown in FIG. 1;
FIG. 6 is a partially sectioned, back elevational view of the
circuit protection device shown in FIG. 1;
FIG. 7 is a schematic view of a circuit protection array comprised
of ten circuit protection devices as shown in FIG. 1;
FIG. 8 is a partially sectioned, perspective view of the circuit
protection device, illustrating a first alternate embodiment of the
present invention;
FIG. 9 is a schematic view of a circuit protection array comprised
of ten circuit protection devices as shown in FIG. 8;
FIG. 10 is an exploded, pictorial view of a circuit protection
device illustrating a second alternate embodiment of the present
invention;
FIG. 11 is a cross-sectional, front view of the circuit protection
device shown in FIG. 10;
FIG. 12 is a cross-sectional, plan view of the circuit protection
device shown in FIG. 10;
FIG. 13 is a cross-sectional, side view of the circuit protection
device shown in FIG. 10;
FIG. 14 is a partially sectioned, front view of the circuit
protection device shown in FIG. 10, showing the device after it has
been "triggered" by a fault condition;
FIG. 15 is a partially sectioned, side view of the circuit
protection device shown in FIG. 14;
FIG. 16 is a schematic view of a circuit protection array comprised
of ten circuit protection devices as shown in FIG. 10; and
FIG. 17 is a perspective view of a circuit protection device and
base assembly, illustrating another embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to the drawings wherein the showings are for the
purpose of illustrating a preferred embodiment of the invention
only, and not for the purpose of limiting same, FIG. 1 is an
exploded perspective view of a transient voltage suppression device
10 for use with a power distribution system for preventing voltage
fault conditions from reaching a sensitive circuit load.
Voltage suppression device 10 is generally comprised of a voltage
sensitive element 12 that is contained within a housing 20. Housing
20 is comprised of a base section 22 and a cover section 24. Base
section 22 is adapted to receive and hold the operative elements of
a voltage suppression device 10. To this end, base section 22
includes a generally planar bottom wall portion 32. A generally
U-shaped structure, comprised of a hack wall 34 and opposed side
walls 36, extends from bottom wall 32. Side walls 36 are formed to
define a cavity 42 adjacent to back wall 34. Cavity 42 is
dimensioned to receive voltage sensitive element 12. In the
embodiment shown, voltage sensitive element 12 is rectangular in
shape, and therefore, cavity 42 is rectangular in shape. As will be
appreciated by those skilled in the art, voltage sensitive element
12 may be cylindrical in shape, and thus the bottom portion of
cavity 42 may be semi-cylindrical in shape to receive a cylindrical
element.
Referring now to voltage sensitive element 12, in accordance with
the present invention, such element is voltage sensitive and
operable to heat up when a voltage applied across the device
exceeds a preselected voltage. In accordance with the present
invention, voltage sensitive element 12 is preferably comprised of
a metal-oxide varistor.
By way of background, MOVs are primarily comprised of zinc oxide
granules that are sintered together to form a disc. Zinc oxide, as
a solid, is a highly conductive material. However, minute air gaps
or grain boundaries exist between the sintered zinc oxide granules
in a MOV, and these air gaps and grain boundaries inhibit current
flow at low voltages. At higher voltages, the gaps and boundaries
between the zinc oxide granules are not wide enough to block
current flow, and thus the MOV becomes a highly conductive
component. This conduction, however, generates significant heat
energy in the MOV. MOVs are typically classified and identified by
a "nominal voltage." The nominal voltage of an MOV, typically
identified by V.sub.N(DC), is the voltage at which the device
changes from an "off state" (i.e., the state where the MOV is
generally non-conductive) and enters its conductive mode of
operation.
Importantly, this voltage is characterized at the 1 mA point and
has specified minimum and maximum voltage levels, referred to
hereinafter as V.sup.MIN and V.sub.MAX respectively. By way of
example, and not limitation, a metal-oxide varistor (MOV) having a
nominal varistor voltage, V.sub.N(DC), of 200 volts may actually
exhibit a change from its generally non-conductive to its
conductive state at a voltage between a minimum voltage, V.sub.MIN,
of 184 volts and a maximum voltage, V.sub.MAX, of 228 volts. This
range of operating voltages for a MOV of a rated nominal voltage
V.sub.N(DC) is the result of the nature of the device. In this
respect, the actual voltage value of a MOV basically depends on the
thickness of the MOV and on the number and size of the zinc oxide
granules disposed between the two electrode surfaces. At the
present time, it is simply impossible, because of the construction
and composition of metal-oxide varistors, to produce identical
devices having identical operating characteristics.
Thus, although MOV 12 of over-voltage protection device 10
preferably has a rated "nominal voltage" V.sub.N(DC) at 1 mA, the
actual voltage at which MOV 12 and every other MOV changes from a
non-conducting state to a conducting state may vary between a
V.sub.MIN and a V.sub.MAX for the rated nominal voltage value. In
the context of the present invention, the minimum voltage V.sub.MIN
of the selected MOV 12 is important, as will be discussed in
greater detail below.
Referring again to base section 22 of housing 20, as best seen in
FIGS. 1 4, cavity 42 is dimensioned to be significantly deeper
(i.e. thicker) than the thickness of MOV 12, for reasons that shall
be described in greater detail below.
Each sidewall 36 includes a slot 44 that is spaced from cavity 42
to define a wall or rail 46 of predetermined thickness. Slots 44 in
opposed side walls 36 are aligned with each other and extend a
predetermined length from the free, upper ends of side wall 36
toward bottom wall 32.
A pair of contact elements 52, 54 are provided for electrical
attachment to the opposite sides of MOV 12. Referring now to FIGS.
2 4 and 6, contact element 54 includes a generally V-shaped body,
designated 54a, having a generally flat mid-section 54b and a flat
elongated leg portion 54c extending from one end thereof. Contact
element 54 is dimensioned such that mid-section 54b is attached to
surface 12b of MOV 12 by an electrically conductive material,
designated 58 in the drawings. Conductive material 58 is preferably
formed of a high temperature, metallic solder such as silver, lead
or alloys thereof. With mid-section 54b attached to surface 12b of
MOV 12, leg portion 54c is dimensioned to extend through an opening
in bottom wall 32 of base section 22 and to project therefrom. The
projecting portion of leg portion 54c is provided as a negative
lead for attachment to a ground or neutral line on an electrical
circuit, as shall be described hereinafter. In accordance with one
aspect of the present invention, contact element 54 is formed of a
spring metal. As best seen in FIGS. 2 and 3, contact element 54 is
disposed between MOV 12 and back wall 34 of base section 22.
V-shaped body portion 54a of contact element 54 is dimensioned to
force MOV 12 away from back wall 34 when MOV 12 is inserted into
cavity 42. In other words, in addition to being an electrically
conductive component, contact element 54 acts as a spring to force
MOV 12 away from back wall 34 into contact with rail 46. As
indicated above and best seen in FIGS. 2 and 3, cavity 42 is
significantly wider than the thickness of MOV 12.
In accordance with one aspect of the present invention, cavity 42
and contact element 54 allow housing 20 to receive MOVs of
different thicknesses. In this respect, many MOVs are formed to
have the same overall shape, but vary only in thickness. The
thickness of the MOV determines the rated "nominal voltage"
V.sub.N(DC) of MOV 12. By providing a deep cavity 42 and contact
element 54 having a spring biasing feature, different MOVs 12 of
varying thicknesses may be used in housing 20, thereby enabling the
formation of a voltage suppression device 10 having different
voltage ratings. Regardless of the thickness of the MOV used,
contact element 54 forces the MOV against rail 46, thereby
positioning surface 12a of MOV 12 in the same relative position
within housing 20.
Referring now to FIGS. 1 3 and 5, contact element 52 is best seen.
Contact element 52 is comprised of a short body portion 52a having
an elongated leg portion 52b and an elongated arm portion 52c. As
best seen in FIG. 5, leg portion 52b and arm portion 52c extend
from opposite ends of body portion 52a in opposite directions. As
best seen in FIG. 3, the end of arm portion 52c is bent to define a
flat elbow portion 52d and a flat finger portion 52e. Arm portion
52d and finger portion 52e define a generally J-shaped
configuration at the end of arm portion 52c.
Like contact element 54, contact element 52 is formed of a
conductive spring metal. In a normal configuration, body portion
52a, leg portion 52b and arm portion 52c are flat and lie in the
same general plane. Elbow portion 52d and finger portion 52e are
bent to one side of this plane. Contact element 52 is mounted to
base section 22 in a generally rectangular mounting boss 72 that
extends from both bottom wall 32 and a side wall 36. Mounting boss
72 includes a slot 74, best seen in FIG. 1, dimensioned to receive
body portion 52a. An opening that communicates with slot 74 extends
through bottom wall 32. The opening is dimensioned to receive leg
portion 52b of contact element 52. Slot 74 is dimensioned such that
contact element 52 may be press-fit into mounting boss 72, with a
portion of leg portion 52b extending through and beyond bottom wall
32 of base section 22, as seen in FIGS. 2 and 3. Contact element 52
is dimensioned such that arm portion 52c extends from mounting boss
72. In accordance with the present invention, arm portion 52c is
forced hack toward MOV 12 and is held in position by a solder
material 82 that secures planar elbow portion 52d to surface 12a of
MOV 12. Unlike high temperature solder 58, solder material 82 is
preferably formed of a material that has a relatively low softening
temperature or melting temperature. A melting temperature, metal
alloy or a polymer having a low softening temperature may be used.
Specifically, solder material 82 is preferably a solid at room
temperature (25.degree. C.), and is a solid up to temperatures
around 35.degree. C. Preferably solder material 82 has a melting
temperature or a softening temperature of between about 70.degree.
C. and about 140.degree. C., and more preferably, has a melting
temperature or a softening temperature of between about 90.degree.
C. and about 100.degree. C.
In the embodiment shown, solder material 82 is formed of an
electrically conductive material or fusible alloy that has a
melting temperature of about 95.degree. C. The exposed surface of
the zinc oxide granules of MOV 12 allows the solder material 82 to
adhere to the surface of MOV 12. When soldered to MOV 12, arm
portion 52c of contact element 52 is in a first position, best seen
in FIG. 2. Absent solder material 82, arm portion 52c would move
away from MOV 12 to its normal planar configuration aligned with
body portion 52a and leg portion 52b. Solder material 82, thus
maintains contact element 52 in electrical contact with surface 12a
of contact MOV 12. In this respect, contact element 52 is adapted
to be a positive lead that is connectable to a power line of a
circuit as shall be hereinafter be described.
As best seen in FIG. 2, finger portion 52e of contact element 52 is
dimensioned to traverse a plane defined by opposing slots 44 in
side walls 36. More specifically, finger portion 52e is dimensioned
to support an arc shield 88. Arc shield 88 is a rectangular plate
formed of an electrically non-conductive material such as plastic,
glass, ceramics or a composition thereof. Arc shield 88 dimensioned
to be freely slideable within slots 44. With finger portion 52e of
contact element 52 maintained in its first position, arc shield 88
rests upon finger portion 52e and is maintained in a first position
at the upper end of slot 44, as best seen in FIG. 2.
Cover portion 24 of housing 20 is generally rectangular in shape
and defines a cavity that is dimensioned to enclose base section 22
and the components mounted thereon. Cover section 24 is adapted to
be attached to base section 22. Cover section 24 and base section
22 are preferably formed of a molded plastic material and may be
joined by ultrasonic welding. In the embodiment shown, apertures 26
are formed in cover section 24 to receive tabs 28 projecting from
side walls 36 of base section 22, as seen in FIG. 5. Cover section
24 is secured to base section 22 in snap lock fashion as is
conventionally known.
Referring now to the operation of voltage suppression device 10,
one or more voltage suppression devices 10 may be used together to
protect a circuit against an over-voltage fault. FIG. 7
schematically shows a voltage suppression system 90 comprised of
ten voltage suppression devices 10. Each voltage suppression device
10 in system 90 has the same rated "nominal voltage" V.sub.N(DC)
and a peak current surge rating. The current surge protection
afforded by system 90 is thus ten roughly times the peak current
surge rating of a voltage suppression device 10 used in system 90.
For example, if each voltage suppression device 10 has a peak
current surge rating of 10,000 amps, system 90 has a peak current
surge rating of 100,000 amps. As indicated above, although each
voltage suppression device 10 may have the same "rated nominal
voltage," in actuality, the "rated nominal voltage" of each of the
MOVs within a voltage suppression device 10 may vary between a
V.sub.MIN and a V.sub.MAX. As a result, the current surge
experienced by each voltage suppression device 10 may not occur at
the same instant, as shall hereinafter be described.
Each voltage suppression device 10 is connected across a power line
designated 92 and a ground or neutral line designated 94.
Specifically, contact element 52 of each voltage suppression device
10 is connected to power line 92 and contact element 54 of each
voltage suppression device 10 is connected to ground or neutral
line 94. In the embodiment of voltage suppression system 90 shown,
a fuse element 96 precedes suppression system 90 and power line 92
to prevent an over-current condition in excess of what system 90
can handle from reaching system 90 and the circuit to be protected
(not shown). In the system described above, i.e., a system 90
having ten voltage suppression devices 10, each having a peak
current surge rating of 10,000 amps, fuse element 96 would have a
current rating of about 100,000 amps. When connected as shown in
FIG. 7, MOV 12 of each voltage suppression device 10 senses the
voltage across power line 92 and ground or neutral line 94. Absent
any over-voltage fault condition, each voltage suppression device
10 has a first state, as depicted in FIG. 2, wherein elbow portion
52d of contact element 52 is in electrical contact with surface 12a
of MOV 12 through low temperature solder material 82.
During a fault, an over-current condition or an over-voltage
condition may appear. In the event of a high over-current condition
that is in excess of the total peak current surge ratings for all
devices 10 in system 90, fuse element 96 will open, thereby
disconnecting system 90 from the electrical supply and preventing
damage to the system components. In the event of an over-voltage
condition or repetitive pulse condition, MOVs 12 of voltage
suppression devices 10 will experience an overvoltage condition.
When this occurs, thermal energy is created by the surge current
and each MOV 12 begins absorbing energy and dissipating such energy
as heat. As the voltage across an MOV 12 becomes larger, electrical
conductivity of the MOV 12 increases and increased amounts of heat
are thereby generated. As indicated above, because the actual
characteristics of each MOV 12 are not identical, one MOV will have
a lower energy rating and a faster thermal response time as
contrasted to the others. Thus, various MOVs will heat up more
rapidly than other MOVs within voltage suppression system 90. If
the fault condition is severe enough, the MOV of one or more
voltage suppression devices 10 will heat up to the melting
temperature of low temperature solder material 82. When this
occurs, arm portion 52c of contact element 52 is no longer held in
its first position (as shown in FIG. 2). When solder material 82
melts, arm portion 52c is free to move away from surface 12a of MOV
12, as the spring metal material forming contact element 52 seeks
to return to its normal planar configuration. As arm portion 52c
moves away from MOV 12, the conductive path through MOV 12 is
broken thus effectively taking the related circuit suppression
device 10 "off-line." At the same time, arm portion 52c of contact
element 52 breaks away from MOV 12, it also moves away from and no
longer supports arc shield 88. Without the support or arm portion
52c, arc shield 88 drops down to the bottom of slot 44 under the
influence of gravity to a position wherein arc shield 88 is
disposed between arm portion 52c and surface 12a of MOV 12. In this
position, shield 88 prevents subsequent arcing between arm portion
52c and MOV 12.
When one voltage suppression device 10 drops "off-line," the
current surge rating of the entire suppression system 90 is
reduced. Using the example set forth above, if one voltage
suppression device 10 drops "off-line," system 90 will lose the
10,000 ampere surge capability of the dropped device 10, but would
still have a current surge rating of 90,000 amps, until such time
as the off-line suppression device 10 is replaced.
The present invention thus provides a voltage suppression device 10
that may be used alone or in conjunction with other similar devices
to form a voltage suppression system. Device 10 is a self-contained
unit that is operable to suppress voltage spikes in a circuit and
drop off-line when the voltage spike significantly exceeds the
rated nominal voltage of the device to be protected thereby
preventing catastrophic failure of the same.
Referring now to FIG. 8, an alternate embodiment of the present
invention is shown. FIG. 8 basically shows a base section 22 having
MOV element 12 and contact elements 52 and 54 mounted thereto. The
device shown in FIG. 8 is essentially the same as the embodiment
previously described with respect to FIGS. 1 6, the difference
being that a third contact element designated 56 is provided.
Contact element 56 is a straight flat strip of a conductive metal.
Contact element 56 is secured to surface 12a of MOV 12 by a
high-temperature solder 68 that is similar to the high-temperature
conductive material 58 securing contact element 54 to surface 12b
of MOV 12. Contact element 56 is dimensioned to extend through an
opening (not shown) in bottom wall 32 and to project therebeyond.
Contact element 56 provides an indicator lead that is attachable to
an indicator device such as a light, alarm or the like, or may be
used as a lead attached to a computer terminal to monitor the
"state" of voltage suppression device 10. In this respect, so long
as elbow portion 52d remains in contact with surface 12a of MOV 12,
power sensed by contact 52 is connected to contact element 56 along
the conductive surface 12a of MOV 12. In the event of an
over-voltage condition wherein elbow portion 52d of contact element
52 disconnects from surface 12a of MOV 12, current to contact
element 56 ceases. This change of state from a conductive state to
a non-conductive state may be used to provide an indication of when
voltage suppression device 10 has been tripped.
In this respect, FIG. 9 shows voltage suppression system 90, as
previously shown in FIG. 7, including contact element 56 connected
to an indicator, designated 98. By way of example, the fourth
voltage sensitive suppression device 10 from the left is shown
"tripped" (i.e. elbow portion 52d has moved away from surface 12a)
an indicator 98 is shown as non-illuminated. As indicated above,
contact element 56 may be connected to a remote monitoring system
that is operable to detect the change in electrical condition of
contact element 56 and thereby provide an indication of the voltage
suppression devices 10 in array 90 has "tripped" and needs
replacement.
The embodiments shown heretofore are adapted for use in a specific
orientation. In this respect, arc shield 88 is operable under
gravity to move to an insulating position between arm portion 52c
and surface 12a of MOV 12. It will of course be appreciated that
some applications may require positioning of a voltage suppression
device 10 in other than an upright position.
FIGS. 10 15 show a transient suppression voltage device 100,
illustrating an alternate embodiment of the present invention that
is operable in any orientation and that includes means for
providing visual and electronic indications of a "tripped"
device.
Voltage suppression device 100 is generally comprised of a voltage
sensitive element 112 that is contained within housing 120. Housing
120 is comprised of a base section 122 and a cover section 124.
Base section 122 is adapted to receive and hold the operative
elements of voltage suppression device 100. To this end, base
section 122 includes a planar bottom wall portion 132 and a
generally U-shaped structure comprised of a back wall 134 and
opposed sidewalls 136 that extend from bottom wall 132. A slotted
rail 138 is formed along the inner surface of each sidewall 136.
Rails 138 are disposed in alignment with each other and extend
generally perpendicularly from bottom wall 132. A cylindrical
cavity, designated 138a, is defined at the bottom of the slot in
slotted rails 138. Cavity 138a is dimensioned to receive a
compression spring 139, as best seen in FIG. 10. A short wall
section 142 extends between sidewalls 136. Wall section 142 is
disposed to one side of the slot in slotted rails 138, and includes
a centrally located, rectangular notched area 143. A cavity 144 is
defined between short wall 142 and back wall 134. Cavity 144 (see
FIG. 12) is dimensioned to receive voltage sensitive element 112.
Voltage sensitive element 112 is a metal oxide varistor (MOV) of
the type heretofore described in the prior embodiment. Voltage
sensitive element 112 is preferably rectangular in shape to fit
within cavity 144, but may also be cylindrical in shape in which
case the bottom portion of cavity 144 would be semi-cylindrical to
receive the cylindrical MOV.
A pair of electrical contact elements 152, 154 are provided for
electrical attachment to the opposite sides of MOV 112. Contact
element 154, best seen in FIGS. 12 and 13, includes a generally
V-shaped body, designated 154a, having a generally flat mid-section
154b and a flat elongated leg portion 154c (see FIG. 13). Contact
element 154 is dimensioned such that mid-section 154b is attached
to the surface of MOV 112 by an electrically conducting material,
designated 158 in the drawings. Conductive material 158 is
preferably formed of a high temperature metallic solder such as
silver, lead or alloys thereof. Mid-section 154b is attached to the
surface of MOV 112 such that leg portion 154c extends through an
opening in bottom wall portion 132 of base section 122. The
projecting portion of leg portion 154c is provided as a negative
lead for attachment to a ground or neutral line of an electrical
circuit. As discussed in the previous embodiment, contact element
154 is preferably formed of a spring metal to act as a spring to
force MOV 112 away from back wall 134 and into contact against
slotted rails 138.
As best seen in FIG. 11, contact element 152 is comprised of a
short body portion 152a having an elongated leg portion 152b and an
elongated arm portion 152c. Leg portion 152b and arm portion 152c
extend from opposite ends of body portion 152a in opposite
directions. Like contact element 154, contact element 152 is
preferably formed of conductive spring metal. In a normal
configuration, body portion 152a, leg portion 152b and arm portion
152c are flat and lie in the same general plane. Contact element
152 is mounted to base section 122 in a generally rectangular
mounting boss 172 that extends from bottom wall 132 between side
walls 136. Mounting boss 172 includes a slot dimensioned to receive
body portion 152 and an opening through bottom wall 132 that
communicates with the slot. An opening is dimensioned to receive
leg portion 152b of contact element 152. The slot and the opening
in mounting boss 172 are dimensioned such that contact element 152
may be press-fit into mounting boss 172 with a portion of leg
portion 152b extending through and beyond bottom wall portion
132.
As best illustrated in FIG. 13, contact element 152 is dimensioned
such that arm portion 152c extends upward from mounting boss 172.
Arm portion 152c is adapted to be bent backward toward MOV 112 and
to be held against the surface of MOV 112 by a solder material 182,
as best seen in FIG. 13. Arm portion 152c is held in electrical
contact with the surface of MOV 112 by a solder material 182 of the
type heretofore described in the prior embodiment, i.e., a material
that has a relatively low softening temperature.
An arc shield 188 is provided between contact element 152 and MOV
112, as best seen in FIG. 13. Arc shield 188 is basically a flat
plate dimensioned to be freely slideable within the slot defined by
slotted rail 138. Arc shield 188 includes a pair of elongated arms,
designated 188a, that extend upward from the upper edge thereof.
The lower ends of arms 188a are dimensioned to abut compression
springs 139, as best seen in FIG. 14. Arc shield 188 has a first
position, shown in FIG. 13, wherein arc shield 188 is held near
bottom wall portion 132 against the biasing force of compressed
springs 139 by contact element 152. Arc shield 188 is formed of an
electrically nod-conductive material such as plastic, glass,
ceramic or a composition thereof.
As best seen in FIG. 10, a plurality of apertures 192, 194 are
formed in the upper surface of cover 124. Apertures 192 are larger
than apertures 194 and are disposed on cover 124 to be in alignment
with arm portions 188a of arc shield 188 Apertures 192 are
dimensioned to allow arm portions 188a to project therethrough.
Apertures 194 are dimensioned to receive leads from an electrical
switch 198 that is disposed within voltage suppression device 100.
Switch 198 includes an actuator pin 197 and electrical leads 199.
Switch 198 is disposed within cover 124 such that actuating pin 197
is aligned in the plane of arc shield 188. Leads 199 on switch 198
extend through openings 194 and cover 124 for attachment to an
external circuit.
As best seen in FIG. 10, a plurality of apertures 192, 194 are
formed in the upper surface of cover 124. Apertures 192 are larger
than apertures 194 and are disposed on cover 124 to be in alignment
with arm portions 188a of arc shield 188. Apertures 194 are
dimensioned to allow arm portions 188a to project therethrough.
Apertures 194 are dimensioned to receive leads from an electrical
switch 198 that is disposed within voltage suppression device 100.
Switch 198 includes an actuator pin 197 and electrical leads 199.
Switch 198 is disposed within cover 124 such that actuating pin 197
is aligned in the plane of arc shield 188. Leads 199 on switch 198
extend through openings 194 and cover 124 for attachment to an
external circuit.
Referring now to the operation of voltage suppression device 100,
one or more of such devices may be used together to protect the
circuit against an over-voltage fault. In this respect,
over-voltage device 100 may be part of a voltage suppression system
as schematically illustrated in FIG. 16. When connected as shown in
FIG. 16, MOV 112 of each voltage suppression device 100 in the
array senses the voltage across power line 192 and ground or
neutral line 194. Absent an over-voltage fault condition, each
suppression device 100 has a first state as depicted in FIG. 13,
wherein arm portion 152c of contact element 152 is in electrical
contact with the surface of MOV 112 through low temperature solder
182. In this position, contact element 152 maintains arc shield 188
in its first position as shown in FIG. 13. As in the previous
embodiment, during a fault, an over-current condition or
over-voltage condition may appear. In the event of a high
over-current condition, a fuse element 196 will sense the fault and
open, thereby disconnecting the system from the electrical supply
and preventing damage to the system. In the event of an
over-voltage condition or repetitive pulse condition, MOV 112 of
each voltage suppression device 100 will experience the
over-voltage condition. As indicated with the previous embodiment,
if the fault condition is severe enough, MOV 112 in one or more of
the voltage suppression devices 100 will heat up to the melting
temperature of low soldering temperature 182. When this occurs, arm
portion 152c of contact element 152 will be released from the
surface of MOV 112 as solder material 182 melts or softens. Arm
portion 152c is then free to move away from surface of MOV 112, as
the natural spring of metal forming element 152 seeks to return it
to its normal, planar configuration. As arm portion 152c moves away
from MOV 112, the conductive path through MOV 112 is broken, thus
effectively taking the related circuit suppression device 100
"off-line." At the same time arm portion 152c of contact element
152 breaks away from MOV 112, it is also separated from MOV 112 by
arc shield 188. In this respect, because arc shield 188 is no
longer constrained to its first position by arm 152c, it moves
upward thereby forming a barrier between contact element 152 and
MOV 112. As arc shield 188 moves upward under the influence of
biasing springs 139, arm portions 188a project through openings 194
in cover 124, thereby providing a visual indication that device 100
has been triggered, as illustrated in FIGS. 14 and 15. In addition,
the upper edge of arc shield 188 contacts switch-actuating pin 197
of switch 198 thereby actuating switch 198. Switch 198 may control
a local indicator (not shown) to provide an indication of the
condition of voltage suppression device 100, or provide a signal to
a remote location to provide an indication of the condition of
voltage suppression device 100.
Voltage suppression device 100 thus provides a self contained unit
that is operable to suppress voltage spikes in the circuit, and to
drop off-line when the voltage is significantly higher than the
rated voltage of the device thereby preventing catastrophic failure
of voltage suppression device 100. Voltage suppression device 100
is operable in any orientation and provides both a visual
indication of the condition of voltage suppression device 100, as
well as an electrical signal to an external circuit or device that
is indicative of the condition of device 100.
Referring now to FIG. 17, a modification to voltage suppression
device 100 is shown. In FIG. 17, a voltage suppression device,
designated 100', illustrates an alternate embodiment of the present
invention. Voltage suppression device 100' is similar in all
respects to voltage suppression device 100 as heretofore described,
with the exception that voltage suppression device 100' includes
tabs 202 that extend outwardly from base section 122 (only one tab
202 is shown in FIG. 17). In FIG. 17, like components to those
previously described bear like reference numbers.
Tabs 202 are provided to allow voltage suppression device 100' to
be locked into a base 210. Base 210 is generally rectangular in
shape, and includes a flat bottom wall 212 and short side walls
214. A first conductive leg 216 extends from base 210 and is
attached to ground or neutral line 94. A second conductive leg 218
extends from bottom wall 212 and is electrically connected to power
line 92. In the embodiment shown, legs 216, 218 are generally
L-shaped and attached to ground or neutral line 94 and power line
92 by fasteners 219. Base section 210 includes a first pair of
spaced apart openings 222, 224 that extend through bottom wall 212
adjacent conductive legs 216, 218. Openings 222, 224 are
dimensioned to receive contact leg portions 154c, 152b of voltage
suppression device 100'. Openings 222, 224 allow contact legs 154c,
152b to come into electrical contact with conductive leg portions
216, 218, and to be electrically connected to ground or neutral
line 94 and power line 92, respectively. A second pair of openings
226, 228 is formed in opposed side walls 214. Openings 226, 228 are
adapted to receive tabs 202 on voltage suppression device 100' to
allow voltage suppression device 100' to be snapped into base 210.
As indicated above, when voltage suppression device 100' is
attached to base 210, contact legs 152b, 154c are in electrical
contact with power line 92 and ground or neutral line 94,
respectively.
Base 210 is provided for permanent attachment to power line 92 and
ground or neutral line 94 Voltage suppression device 100' is thus
replaceable in the event that voltage suppression device 100'
exceeds its voltage rating and opens the circuit. When voltage
suppression device 100' has "tripped," it may easily replaced by
removing it from base 210 and replacing it with another voltage
suppression device 100' of like rating. In this respect, in
accordance with another aspect of the present invention, there is
preferably provided indication means for insuring that a voltage
suppression device 100' of a particular size when removed from base
210 is replaced with another voltage suppression device 100' of the
same size and voltage rating. Preferably, some type of indication
means is provided on both voltage suppression device 100' and base
210 to insure a proper matching of voltage suppression device 100'
to base 210. In FIG. 17, like reference numbers, i.e., "100," are
provided on both the voltage suppression system and voltage
suppression device 100'.
The embodiment shown in FIG. 17 thus provides a simple, quick and
convenient method of replacing a voltage suppression device once it
has triggered.
The foregoing describes preferred embodiments of the present
invention. It should be appreciated that these embodiments are
described for purposes of illustration only, and that numerous
alterations and modifications may be practiced by those skilled in
the art without departing from the spirit and scope of the
invention. It is intended that all such modifications and
alterations be included insofar as they come within the scope of
the invention as claimed or the equivalents thereof.
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