Field of the Invention
[0001] 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
[0002] 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.
[0003] 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.
[0004] When exposed to voltages exceeding their voltage value, MOVs become highly conductive
devices that absorb and dissipate the energy related to the over-voltage 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.
[0005] In
U.S. Patent 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.
[0006] U.S. Patent No. 6,256,183 to Mosesian et al. discloses a circuit protection device that drops offline when
an MOV within the device senses a voltage surge exceeding the voltage rating of the
MOV. Both of the foregoing devices are designed to be connected between a service
line and a ground line or neutral line, or between a neutral line and a ground line.
[0007] The present invention provides a circuit protection device and a transient voltage
surge suppression system incorporated within a tubular casing for use in protecting
an electrical system from catastrophic failure due to excessive over-voltage conditions
or repetitive fault conditions along such line.
Summary of the Invention
[0008] In accordance with a preferred embodiment of the present invention, there is provided
a disposable voltage suppression device for suppressing voltage surges in an electrical
circuit. The device is comprised of a tubular casing formed of an electrically insulating
material. A first conductive component is attached to a first end of the casing. A
second conductive component is attached to a second end of the casing. A tubular voltage
sensitive assembly is disposed within the tubular casing. The voltage sensitive assembly
is comprised of two or more tubular sections. The voltage sensitive assembly has a
first surface and a second surface and a predetermined voltage rating across the first
and second surfaces. The voltage sensitive assembly increases in temperature as voltage
applied across the first and second surfaces exceeds the voltage rating. A first terminal
is electrically connected to the first surface of the voltage sensitive assembly and
to the first conductive component. A thermal element is electrically connected to
the second surface of the voltage sensitive assembly. The thermal element is an electrically
conductive solid at room temperature and has a predetermined softening temperature.
A second terminal is electrically connected to the second conductive component. The
second terminal has a contact portion in electrical connection with the second surface
of the voltage sensitive assembly. The voltage sensitive assembly senses the voltage
drop between the first conductive element and the second conductive element. The second
terminal is maintained in electrical contact with the voltage sensitive assembly by
the thermal element and is biased away therefrom, wherein the second terminal moves
away from electrical contact with the voltage sensitive assembly and breaks the electrical
current path if an over-voltage condition sensed by the voltage sensitive assembly
exceeds the voltage rating of the voltage sensitive assembly and causes the voltage
sensitive assembly to heat the thermal element beyond its softening point. An arc
shield is movable from a first position wherein the arc shield allows contact between
the contact portion of the second terminal and the voltage sensitive assembly to a
second position wherein the shield is disposed between the contact portion of the
second terminal and the voltage sensitive assembly when the second terminal moves
from electrical contact with the voltage sensitive assembly.
[0009] 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 tubular casing formed of an electrically insulating material. A
first conductive component is attached to a first end of the casing. A second conductive
component is attached to a second end of the casing. Two or more tubular sections
are provided. Each of the tubular sections 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 tubular sections between the first conductive
component and the second conductive component. A normally closed, thermal switch is
comprised of one end of one of the terminals, a surface of the tubular sections and
a thermal element. The one end of one of the terminals is maintained in electrical
contact with the surfaces of the tubular sections by the thermal element. The thermal
switch is electrically connected in series with the tubular sections between one of
the conductive components and the tubular sections. The thermal switch is thermally
coupled to the tubular sections wherein the one of the terminals moves from a normally
closed position where the one of the terminals is maintained in electrical contact
with the surfaces of the tubular sections to an open position where the one of the
terminals moves out of electrical contact with the surfaces of the tubular sections
to form a gap between the one of the terminals and the tubular sections when the temperature
of the tubular sections reaches a level causing the thermal element to soften. The
one of the terminals includes a contact portion and a second portion that extends
away from the contact portion. A non-conductive barrier is operable to move into the
gap when the one of the terminals moves to an open position. The barrier prevents
line voltage surges from arcing between the one of the terminals and the tubular sections.
The second portion of the one of the 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 the thermal element begins to soften.
The non-conductive barrier is biased toward the thermal element, but is constrained
from movement toward the thermal element by contact with the second portion of the
one of the terminals at a location that is spaced away from the contact portion, until
the thermal element begins to soften.
[0010] 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 tubular casing formed of an electrically insulating material. A
first conductive component is attached to a first end of the casing. A second conductive
component is attached to a second end of the casing. A tubular voltage sensitive assembly
is disposed within the casing. The voltage sensitive assembly is comprised of two
or more tubular sections. The voltage sensitive assembly has a first surface and a
second surface and a predetermined voltage rating across the first and second surfaces.
The voltage sensitive assembly increases in temperature as voltage applied across
the first and second surfaces exceeds the voltage rating. A first terminal is electrically
connected to the first surface of the voltage sensitive assembly and the first conductive
component. A thermal element is electrically connected to the second surface of the
voltage sensitive assembly. The thermal element is an electrically conductive solid
at room temperature and has a predetermined softening temperature. A second terminal
is formed of a spring metal having one end in electrical connection with the second
surface of the voltage sensitive assembly and another end connected to the second
conductive component. The voltage sensitive assembly senses a voltage drop between
the first conductive component and the second conductive component. The second terminal
is bent from a normal and relaxed configuration to be maintained in contact with the
voltage sensitive assembly by the thermal element. The second terminal is inherently
biased away from the voltage sensitive assembly toward the normal and relaxed configuration,
wherein the second terminal springs away from electrical contact with the voltage
sensitive assembly softens and breaks the electrical current path if an over-voltage
condition sensed by the voltage sensitive assembly exceeds the voltage rating of the
voltage sensitive assembly and causes the voltage sensitive assembly to heat the thermal
element beyond its softening point. An arc shield is movable from a first position
wherein the arc shield allows contact between the second terminal and the voltage
sensitive assembly to a second position wherein the arc shield is disposed between
the second terminal and the voltage sensitive assembly when the second terminal moves
from electrical contact with the voltage sensitive assembly. The second terminal has
a contact portion for making electrical contact with the thermal element and a second
portion. The second portion extends through the path of the arc shield and blocks
the movement of the arc shield until the thermal element reaches its softening point.
[0011] It is an advantage of the present invention to provide a circuit protection device
to protect sensitive circuit components and systems from current and voltage surges.
[0012] It is another advantage 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.
[0013] A further advantage 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.
[0014] Another advantage 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).
[0015] A still further advantage 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.
[0016] A still further advantage 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
line. According to an embodiment, a voltage suppression device for suppressing voltage
surges in an electrical circuit is provided having a voltage sensitive assembly comprised
of a plurality of tubular sections within a tubular casing
[0017] These and other 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
[0018] 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 a partially-sectioned, side elevation view of a fuse-holder showing a tubular,
circuit protection device inserted partially therein.
FIG. 2 is a perspective view of a circuit protection device according to a preferred
embodiment of the present invention, showing the circuit protection device mounted
in a DIN-rail fuse holder;
FIG. 3 is a cross-sectional view of the circuit protection device shown in FIG. 2,
showing the device in a normal operating condition;
FIG. 4 is a cross-sectional view of the circuit protection device shown in FIG. 2,
showing the device after actuation by a fault condition;
FIG. 5 is an exploded, perspective view of the circuit protection device, shown in
FIG. 2;
FIG. 6 is a cross-sectional view taken along lines 5-5 of FIG. 3;
FIG. 7 is a perspective view of a two-piece metal oxide varistor element, according
to another embodiment of the present invention;
FIG. 8 is a cross-sectional view of a circuit protection device having a "tripped-circuit"
indicator, illustrating another embodiment of the present invention;
FIG. 9 is a cross-sectional view showing the circuit protection device of FIG. 8 showing
the device in a "tripped-circuit" condition;
FIG. 10 is an exploded, perspective view of a voltage sensitive assembly comprised
of a plurality of tubular sections for use in a circuit protection device according
to the present invention;
FIG. 11 is an exploded, perspective view of another embodiment of the voltage sensitive
assembly shown in FIG. 10;
FIG. 12 is an exploded, perspective view of yet another embodiment of the voltage
sensitive assembly shown in FIG. 10;
FIG. 13 is an exploded, perspective view of still another embodiment of the voltage
sensitive assembly shown in FIG. 10; and
FIG. 14 is an exploded, perspective view of a further embodiment of a voltage sensitive
assembly for use in a circuit protection device.
Detailed Description of Preferred Embodiment
[0019] 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 shows a circuit protection device 10, according to a preferred embodiment of
the present invention, within a conventional, fuse holder 12. Fuse holder 12, in and
of itself, forms no part of the present invention, but shall be described briefly
to illustrate a preferred manner of use of a circuit protection device 10.
[0020] Fuse holder 12 is comprised of a molded, polymer housing 14 having leg portion 14a,
14b formed along the lower surface thereof. Leg portion 14a, 14b are designed to allow
housing 14 to be attached, in snap-lock fashion to a mounting rail (not shown), wherein
spaced-apart leads (not shown) that form part of an electrical circuit come into electrical
contact with spaced-apart pairs of contact blades 24. A receiver 16 is pivotally mounted
to housing 14 by a pin 17. Receiver 16 includes an elongated slot 16a that is dimensioned
to receive a cylindrical fuse (not shown) or a circuit protection device 10 according
to the present invention.
[0021] Receiver 16 is pivotally movable to housing 14 and is movable between an opened position,
as shown in FIG. 1, and a closed position, wherein the ends of a fuse or circuit protection
device 10 are in electrical contact with contact blades 24, as will be better understood
from a further reading of the present specification.
[0022] In FIG. 2, circuit protection device 10 is shown mounted to a conventional DIN-rail
fuse mount 20 having a base 22 and spaced-apart pairs of contact blades 24.
[0023] Circuit protection device 10 is generally comprised of a tubular, insulated casing
32 that defines an inner bore or cavity 34. Bore or cavity 34 extends axially through
casing 32. In the embodiment shown, casing 32 has a cylindrical shape and defines
a cylindrical, inner cavity 34. Casing 32 has a predetermined wall thickness. In the
embodiment shown, cylindrical tube casing 32 defines a cylindrical outer surface 36.
The distal ends of casing 32 are formed to have two defined wall areas 38 of reduced
thickness. Annular grooves or recesses 42 are cut in outer surface 36 of casing 32,
as best seen in FIG. 5. These annular grooves or recesses 42 are spaced from wall
areas 38 of reduced cross section.
[0024] Disposed within the casing is a voltage sensitive element (MOV) 52, having an outwardly
facing, first surface 52a, and an inwardly facing, second surface 52b. In the embodiment
shown, the voltage sensitive element (MOV) 52 is tubular in shape, wherein the cylindrical
outer surface of the voltage sensitive element (MOV) 52 defines first surface 52a
and the cylindrical inner surface of voltage sensitive element (MOV) 52 defines second
surface 52b. Voltage sensitive element (MOV) 52 is dimensioned to fit within casing
32. Voltage sensitive element (MOV) 52 has an axial length slightly less than the
axial length of casing 32, as shall be described in greater detail below.
[0025] In accordance with the present invention, voltage sensitive element (MOV) 52 is,
as its name implies, 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 (MOV) 52 is preferably comprised of a metal-oxide varistor
(MOV).
[0026] By way of background, metal oxide varistors (MOVs) are primarily comprised of zinc
oxide granules that are sintered together. In the embodiment shown, the zinc oxide
granules are sintered together to form a cylindrical tube. 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 an MOV, and these air gaps and grain boundaries
inhibit current flow at low voltage. 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
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 hereafter as V
MIN and V
MAX respectively. By way of example, and not limitation, a metal-oxide varistor (MOV)
having a nominal varistor voltage, V
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
MIN, of 184 volts and a maximum voltage, V
MAX, of 228 volts. This range of operating voltages for an MOV of a rated nominal voltage
V
N(DC) is the result of the nature of the device. In this respect, the actual voltage value
of an 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 (MOVs), to produce identical devices having identical operating characteristics.
[0027] Thus, although voltage sensitive element (MOV) 52 of circuit protection device 10
preferably has a rated "nominal voltage" V
N(DC) at 1 mA, the actual voltage at which the MOV and every other MOV changes from a non-conducting
state to a conducting state may vary between a V
MIN and a V
MAX for the rated nominal voltage value. In the context of the present invention, the
minimum voltage V
MIN of the selected MOV is important, as will be discussed in greater detail below.
[0028] A second conductive lining 72 is provided to be in electrical contact with second
surface 52b of voltage sensitive element (MOV) 52. In the embodiment shown, second
conductive lining 72 is tubular in shape and is dimensioned to be positioned adjacent
to and in contact with the inwardly facing, second surface 52b of voltage sensitive
element (MOV) 52. Second conductive lining 72 is dimensioned such that at least a
portion of lining 72 extends along the central portion of voltage sensitive element
(MOV) 52. In the embodiment shown, second conductive lining 72 is cylindrical in shape
and has a length at least equal to the length of voltage sensitive element (MOV) 52.
[0029] A first conductive liner 62 is disposed on first surface 52a of voltage sensitive
element (MOV) 52. In the embodiment shown, first conductive liner 62 is comprised
of a tubular element formed of a conductive material, such as metal. In a preferred
embodiment, conductive liner 62 is formed of copper. In the embodiment shown, first
conductive liner 62 has a length essentially equal to the length of voltage sensitive
element (MOV) 52. First conductive liner has an inner diameter that is dimensioned
to closely match the outer diameter of voltage sensitive element (MOV) 52 such that
the inner surface of first conductive lining 62 is in electrical contact with first
surface 52a of voltage sensitive element (MOV) 52 when first conductive lining 62
is positioned over voltage sensitive element (MOV) 52. A first terminal 64 is electrically
connected to first conductive lining 62. In the embodiment shown, first terminal 64
is generally U-shaped. First terminal 64 is dimensioned to wrap around one end of
casing 32, as best seen in FIGS. 3 and 4, with a leg portion 64a of U-shaped first
terminal 64 electrically connected to first conductive lining 62 and another leg portion
64b overlaying and extending parallel to the outer surface of casing 32. As illustrated
in FIGS. 3 and 4, leg portion 64b is disposed adjacent to wall area 38 at the end
of casing 32 where the wall thickness of casing 32 is of reduced thickness. Leg portion
64a of U-shaped terminal 64 is bent inward slightly toward leg portion 64b to define
a slightly flared or widened base portion 64c that is slightly wider than the thickness
of wall area 38.
[0030] Referring now to FIG. 5, a second terminal 74 is comprised of a base portion 76 and
an arm portion 78. In the embodiment shown, base portion 76 has a flat, circular plate-like
configuration and arm portion 78 has an elongated, flat, rectangular strip-like configuration.
In a normal configuration, arm portion 78 extends generally perpendicular from base
portion 76. Base portion 76 and arm portion 78 are preferably integrally formed from
a rigid, electrically conductive, flat, plate-like or sheet-like material. In a preferred
embodiment, second terminal 74, i.e., base portion 76 and arm portion 78, is formed
from a copper plate. The plate-like material forming base portion 76 and arm portion
78 preferably has a thickness such that arm portion 78 is rigid, but the free end
of arm portion 78 can move, i.e., be deflexed, relative to base portion 76 in a manner
that shall be described in greater detail below.
[0031] Base portion 76 has a diameter approximately equal to the diameter of casing 32,
and arm portion 78 has a length wherein the free end thereof is located near the axial
center of casing 32 when circuit protection device 10 is assembled.
[0032] As shown in the drawing, a bend 82 is formed in arm portion 78 near the free end
thereof. Bend 82 defines a contact point 82a to form an electrical connection with
inner surface of second conductive liner 72, as shall be described in greater detail
below.
[0033] Voltage sensitive elements (MOV) 52 with first and second conductive liners 62, 72
are dimensioned to be disposed within casing 32 with the outer surface of first conductive
lining 62 snuggly disposed against the inner surface of casing 32, as best seen in
FIGS. 3 and 4. As shown in the drawings, in the embodiment shown, voltage sensitive
element (MOV) 52 and first and second conductive linings 62, 72 have a length that
is slightly shorter than the length of casing 32. U-shaped first terminal 64 is dimensioned
to wrap around one end of casing 32, with leg portion 64b disposed along the outer
surface of casing 32. Second terminal 74 is dimensioned to be inserted in the other
end of casing 32.
[0034] End caps 92, 94 are provided on the distal ends of casing 32 for locking first and
second terminals within casing 32. Each cap 92, 94 is dimensioned to enclose one end
of casing 32. In this respect, each end cap 92, 94 is cup-shaped and has a circular
base wall portion 96 and a cylindrical side wall portion 98. Caps 92, 94 are attached
to casing 32 by crimping the opened end of side wall portions 98 onto casing 32. As
best seen in FIGS. 3 and 4, the open ends of side wall portions 98 of caps 92, 94
are crimped, such that the free edge of side wall portion 98 of each cap 92, 94 is
forced into an annular recess 42 formed on outer surface 36 of casing 32.
[0035] As best seen in FIG. 3, leg portion 64b of U-shaped first terminal 64 is captured
between wall area 38 of casing 32 and side wall portion 98 of end cap 92, such that
leg portion 64b of first terminal 64 is in electrical contact with metallic end cap
92. In this respect, end cap 92 is in electrical contact with first surface 52a of
voltage sensitive element (MOV) 52 through first terminal 64 and first conductive
lining 62. An insulating disc 112 is disposed within end cap 92. As shown in the drawing,
insulating disc 112 is dimensioned to be disposed on the inner surface of bottom wall
portion 96. Insulating disc 112 is formed of an electrically insulating material and
is provided basically to ensure end cap 92 is electrically isolated from second conductive
lining 72.
[0036] As best seen in FIG. 4, base portion 64c of U-shaped first terminal 64 is enlarged
so as to secure the end of voltage sensitive element (MOV) 52, as well as first conductive
lining 62 that is disposed along the inner surface of voltage sensitive element (MOV)
52 spaced from the end of casing 32. In other words, the ends of voltage sensitive
element (MOV) 52 and first conductive lining 62 are spaced from first insulating disc
112 in the embodiment shown.
[0037] Circular base portion 76 of second terminal 74 is dimensioned to fit within cap 94,
with base portion 76 disposed against, and in electrical contact with, base wall portion
96 of end cap 94.
[0038] A second, insulating disc 114, formed from an insulating material, is provided to
be positioned within end cap 94. Second insulating disc 114 is a flat disc having
a circular outer edge that is dimensioned to fit within end cap 94. An aperture or
hole 116 is formed in the center of insulating disc 114. Aperture 116 is dimensioned
to allow arm portion 78 of second terminal 74 to extend therethrough. In this respect,
insulating disc 114 is designed to be positioned adjacent the ends of casing 32, voltage
sensitive element (MOV) 52, and first and second conductive linings 62, 72. Second
insulating disc 114, essentially, isolates the ends of first and second conductive
linings 62, 72 from base wall portion 96 of end cap 94. Base portion 76 of second
terminal 74 is confined between second insulating disc 114 and bottom wall portion
96 of end cap 94, as best seen in FIGS. 3 and 4.
[0039] When second terminal 74 is initially assembled with casing 32, arm portion 78 of
second terminal 74 extends axially into opening 34 defined within casing 32. As best
seen in FIGS. 3 and 4, the free end of arm portion 78 of second terminal 74 is slightly
bent to define an offset portion. Arm portion 78 of second terminal 74 is designed
to be displaced, i.e., forced, from its normal, first position (as shown in FIG. 4)
to a second position wherein bend 82 formed in arm portion 78, is brought into electrical
contact with the inner surface of second conductive lining 72.
[0040] According to one aspect of the present invention, elongated arm portion 78 of second
terminal 74 is held in the second position (shown in FIG. 3) in electrical contact
with the inner surface of second conductive lining 72 by a thermal element 122. In
a preferred embodiment, thermal element 122 is a solder material that has a relatively
low softening temperature or melting temperature. A low melting temperature metal
alloy or a polymer having a low softening temperature may be used. Thermal element
122 is preferably a solid at room temperature (25°C) and a solid up to a temperature
around 35°C. Preferably, thermal element 122 has a melting temperature or a softening
temperature of between about 70°C and 140°C and, more preferably, has a melting temperature
or softening temperature of between 90°C and about 100°C.
[0041] In one embodiment of the invention, thermal element 122 is comprised of an alloy
comprised of about 52% imdium (Im) and about 48% tin (Sm), has a melt temperature
of about 118°C.
[0042] When attached to second conductive lining 72, as shown in FIG. 3, arm portion 78
of second terminal 74 is elastically deformed (as contrasted with plastically deformed)
to where arm portion 78 is held in place against the inner surface of second conductive
lining 72, but would spring back to approximately its original, normal position, as
shown in FIG. 4, if not restrained by thermal element 122. In other words, because
arm portion 78 is elongated and is formed of a generally rigid metal material, it
has a springlike characteristic. When secured in its second position, as illustrated
in FIG.3, a slot or recess 126 is formed between the contact area of arm portion 78
and the inner surface of second conductive lining 72.
[0043] A barrier element 132 is provided to be movable within casing 32. As shall be described
in greater detail below, barrier element 132 is essentially an arc shield. More specifically,
barrier element 132 is movable within second conductive lining 72. In the embodiment
shown, barrier element 132 is generally a cup-shaped device having a flat circular
base 132a with a cylindrical side wall 132b. Barrier element 132 defines a cylindrical
inner cavity 132c. Cylindrical side wall 132b of barrier 132 is dimensioned such that
barrier 132 is freely slidable within the opening defined by second conductive lining
72. Barrier element 132 is preferably integrally formed of an electrically insulating,
non-conductive material, such as, by way of example and not limitation, a polymer
material. Biasing element 134 biases barrier element 132 toward arm portion 78 of
second terminal 74. When arm portion 78 is held against the inner surface of second
conductive lining 72 by thermal element 122, the edge of side wall 132b of barrier
element 132 is captured by recess or slot 126 formed by the bent end of arm portion
78 and the surface of second conductive lining 72. In the embodiment shown, biasing
element 134 is a compression spring. Arm portion 78, barrier element 132, and compression
spring 134 are dimensioned such that, when the free end of elongated arm 78 is held
against the inner surface of second conductive lining 72, barrier element 132 is prevented
from movement within second conductive lining 72 relative to arm portion 78 by bend
82 of arm portion 78. As shown in FIG. 3, compression spring 132 is compressed and
exerts a biasing force against base 132a of cup-shaped barrier 132 which is prevented
from movement by bend 82 of arm portion 78.
[0044] Referring now to the operation of circuit protection device 10, it is contemplated
that one or more circuit protection devices 10 may be used together to protect an
electrical circuit against a circuit fault condition. While circuit protection device
10 may be used in a conventional DIN-rail fuse mount 20, as shown in FIG. 2, circuit
protection device 10 is preferably used in a fuse holder 12, as shown in FIG. 1. Fuse
holder 12 allows an individual to easily connect a circuit protection device 10 to
the electrical system or circuit to be protected without the individual being exposed
to electrically energized power lines. In other words, a fuse holder 12 allows safe
and easy attachment of a circuit protection device 10 to a "live" circuit, as well
as removal therefrom.
[0045] When circuit protection device 10 is disposed within holder 12, and holder 12 is
in a closed position, caps 92, 94 of circuit protection device 10 are in contact with
contact blades 24 of holder 12. When holder 12 is attached across a power line and
a ground and neutral line of an electrical circuit, a circuit path is created through
circuit protection device 10. More specifically, a circuit path is created from end
cap 92 through first conductive lining 62 and voltage sensitive element (MOV) 52 to
second conductive lining 72. The circuit path continues from second conductive lining
72 through arm portion 78 of second terminal 74 (that is held in contact with second
conductive lining 72 by thermal element 122) to end cap 94. In other words, when holder
12 is attached to a mounting rail (not shown) and circuit protection device 10 is
in electrical contact with contact blades 24, a conductive path is defined between
a power line and a ground or neutral line through circuit protection device 10. As
will be appreciated, a conductive path will be established through circuit protection
device 10 even if the positions of end caps 92, 94 are reversed.
[0046] As indicated above, more than one circuit protection device 10 may be used to protect
an electrical circuit. A circuit protection system may comprise "N" number of circuit
protection devices 10 connected in parallel to a power line and ground or neutral
line. In such a "multiple device system," each circuit protection device 10 has the
same rated "nominal voltage" V
N(DC) and a peak current surge rating. The total current surge protection afforded by such
a multiple device system is thus approximately "N" times the peak current surge rating
of a circuit protection device 10 used in the system. For example, if each circuit
protection device 10 has a peak current surge rating of 10,000 amps, the assembly
has a total peak current surge rating of (10,000 · N) amps. As indicated above, although
each circuit protection device 10 may have the same "rated nominal voltage," in actuality,
the "rated nominal voltage" of each of the MOVs within a circuit protection device
10 may vary between a V
MIN and a V
MAX. As a result, the current surge experienced by each circuit protection device 10
may not occur at the same instant, as shall hereinafter be described.
[0047] In the event of an over-voltage condition or repetitive pulse condition, the voltage
sensitive element (MOV) 52 of a circuit protection device 10 will experience an over-voltage
condition. This over-voltage condition produces a voltage differential (bias) between
first conductive lining 62 and second conductive lining 72 and across first surface
52a and second surface 52b of voltage sensitive element (MOV) 52. When this occurs,
thermal energy is created by the surge current, and each tubular voltage sensitive
element (MOV) 52 begins absorbing energy and dissipating such energy as heat. As the
voltage differential across a voltage sensitive element (MOV) 52 becomes larger, electrical
conductivity of the voltage sensitive element (MOV) 52 increases and increased amounts
of heat are thereby generated. As indicated above, because the actual characteristics
of each voltage sensitive element (MOV) 52 are not identical, one voltage sensitive
element (MOV) 52 in a series arrangement will have a lower energy rating and a faster
thermal response time as contrasted to the others. Thus, various voltage sensitive
elements (MOV) 52 will heat up more rapidly than other voltage sensitive elements
(MOV) 52 within a multiple device system. If the fault condition is severe enough,
the voltage sensitive element (MOV) 52 of one or more circuit protection device 10
will heat up to the melting temperature of low temperature solder material of thermal
element 122. When this occurs, arm portion 78 of second terminal 74 is no longer held
in its first position (as shown in FIG. 3). When thermal element 122 melts, arm portion
78 is free to move away from inner surface 52a of voltage sensitive element (MOV)
52, as the metal material forming second terminal 74 seeks to return to its normal
planar configuration.
[0048] According to one aspect of the present invention, second surface (the inner surface)
52b of voltage sensitive element (MOV) 52 heats faster than first surface (the outer
surface) 52a. This is due to second surface 52b having less surface area than first
surface area 52a, due to the different diameters of the respective surfaces. Because
of its smaller surface area, the current density per unit area, and in turn, the joule
heat per unit area, is higher along second surface 52b than along first surface 52a.
The faster heating of second surface 52b provides melting of thermal element 122 when
fault conditions exist.
[0049] When arm portion 78 moves away from voltage sensitive element (MOV) 52, the conductive
path through circuit protection device 10 is broken, wherein circuit protection device
10 drops "off-line."
[0050] When one circuit protection device 10 drops "off-line," the current surge rating
of the other circuit protection devices 10 in the multiple device system is reduced.
Using the example set forth above, if one circuit protection device 10 drops "off-line,"
the system will lose the 10,000 ampere surge capability, but would still have a current
surge rating of (10,000 · (N-1)) amps, until such time as the off-line circuit protection
device 10 is replaced.
[0051] The present invention thus provides a circuit protection device 10 that may be used
alone or in conjunction with other similar devices to form part of a circuit protection
system. Circuit protection 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.
[0052] Referring now to FIGS. 8 and 9, a circuit protection device 210 illustrating an ultimate
embodiment of the present invention is shown. Circuit protection device 210 in many
respects is the same as circuit protection device 10. In this respect, components
of circuit protection device 210 that are like the components in circuit protection
device 10 are indicated with the same reference numbers. The main difference between
circuit protection device 210 and the aforementioned circuit protection device 10
is that cylindrical barrier element 132 includes an elongated pin 232 extending axially
from flat, circular base 132a of barrier element 132. Pin 232 is dimensioned to extend
through an opening 234 formed through first insulating disk 112 and base wall portion
96 of end cap 92 when barrier element 132 is maintained in the first position against
biasing element 134 by arm portion 78 of second terminal 74, as best seen FIG. 8.
As shown in FIG. 8, end portion 232a of pin 232 extends beyond base wall portion 96
of end cap 92 when circuit protection device 210 is in its normal operating configuration.
In the event of a fault condition that would cause circuit protection device 210 to
"trip," end portion 232a of pin 232 would be withdrawn into the inner bore 34 of casing
32 as biasing element 134 forces barrier element 132 to a "tripped position." Thus,
the absence of the end portion 232a of pin 232 extending from end cap 92 is an indication
that circuit protection device 210 has "tripped" and should be replaced. Circuit protection
device 210 thus provides a quick and simple configuration to provide an indicator
means indicating the condition of circuit protection device 210.
[0053] The foregoing description is a specific embodiment of the present invention. It should
be appreciated that this embodiment is 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. For example,
in the embodiment described heretofore, voltage sensitive element (MOV) 52 is a one-piece
component. FIG. 7 shows a voltage sensitive element 152 formed of two sections 154,
156 that may be used in place of voltage sensitive element (MOV) 52 in circuit protection
device 10. As will be appreciated by those skilled in the art, first and second conductive
linings 62, 72 would maintain sections 154, 156 in the desired tubular configuration
within circuit protection device 10.
[0054] Heretofore, circuit protection device 10 has been described having a voltage sensitive
element 52 comprised of a single elongated tubular member or a voltage sensitive element
152 formed of two (2) semi-cylindrical sections 154, 156. (See FIG. 7.) In accordance
with another aspect of the present invention, FIGS. 10-14 show voltage sensitive assemblies,
designated 252, 252A, 252B, 252C, and 352, that are comprised of an "N" number of
short tubular varistor sections that may be used in place of a single, elongated voltage
sensitive element 52 in a circuit protection device 10.
[0055] FIG. 10 shows a voltage sensitive assembly 252 comprised of short tubular sections
262, 264, 266, 268. In the embodiment shown, tubular sections 262, 264, 266, 268 are
essentially identical and have like inner and outer diameters. Each tubular section
262, 264, 266, 268 is formed of a like varistor material. FIG. 10 illustrates that
the voltage sensitive component within circuit protection device 10 may be comprised
of two or more tubular sections 262, 264, 266, 268. In this respect, shorter tubular
sections 262, 264, 266, 268 are easier and more economical to form, as compared to
a single, elongated voltage sensitive element 52. Moreover, in accordance with another
aspect of the disclosed embodiment, manufacturing a voltage sensitive assembly 252
comprised of a plurality of short tubular sections 262, 264, 266, 268 allows for the
production of voltage suppression devices 10 having different operating characteristics
while using the same basic structural configuration. With voltage sensitive assembly
252, the operating characteristics of circuit protection device 10 can be easily modified
by employing less than all of tubular sections 262, 264, 266, 268 within the space
defined between first and second conductive linings 62, 72 of circuit protection device
10. For example, by eliminating a single tubular section, the amount of MOV material
within circuit protection device 10 is reduced by 25%. Thus, the operating characteristics
of circuit protection device 10 are reduced in relation to the amount of MOV material
of the eliminated tubular section 268.
[0056] FIG. 11 shows a voltage sensitive assembly 252A which is a modification of voltage
sensitive assembly 252. Voltage sensitive assembly 252A is essentially the same as
voltage sensitive assembly 252, with the exception that tubular section 266 is replaced
by a tubular non-conductive insulator 276. Non-conductive insulator 276 has the same
dimensions as tubular section 266.
[0057] Non-conductive insulator 276 is inserted in place of tubular section 266 to maintain
the overall structural integrity of circuit protection device 10. Since the outer
and inner surfaces of tubular sections 262, 264, 266 are each in contact respectively
with inner surface of first conductive lining 62 and the outer surface of second conductive
lining 72, non-conductive insulator 276 may be provided at any location within the
space defined between first and second conductive linings 62, 72. In other words,
non-conductive insulator 276 may be provided at an end of the tubular section 262,
264, and 268, or between tubular section 262 and tubular section 264, or between tubular
section 264 and tubular section 268 (as shown in FIG. 11), without affecting the operating
characteristics of circuit protection device 10.
[0058] Referring now to FIG. 12, another modification to voltage sensitive assembly 252
is shown. FIG. 12 shows a voltage sensitive assembly 252B which is the same as voltage
sensitive assembly 252 with the exception that tubular section 264 of voltage sensitive
assembly 252 is replaced with a tubular section 284 that is formed of a metal oxide
varistor material that is different from the varistor material forming tubular sections
262, 266, 268. By varying the composition of one or more of the tubular sections within
a circuit protection device 10, the overall operating characteristics of a voltage
sensitive assembly 10 can be varied.
[0059] The foregoing illustrates how circuit protection device 10 may be modified to have
different operating characteristics by merely modifying the number and/or type of
tubular sections 262, 264, 266, 268 disposed within circuit protection device 10.
[0060] As will be appreciated by those skilled in the art, the dimensions of the respective
tubular sections 262, 264, 266, 268 (i.e., the volume and mass of the material forming
these sections) establish the operating characteristics of each of the sections. FIG.
13 illustrates how the dimensions of a tubular section can further be modified to
vary the operating conditions of the section. FIG. 13 shows a voltage sensitive assembly
252C having a tubular section 294 that includes an inner portion 294a comprised of
a varistor material and an outer portion 294b comprised of a conductive material.
As illustrated in the drawings, the inner portion 294a of tubular section 294 is tubular
in shape and has a wall thickness that is thinner than tubular sections 262, 264,
266, 268 heretofore described. Outer portion 294b is tubular in shape and is dimensioned
to maintain electrical contact with the inner surface of first conductive lining 62
of current protection device 10. By providing a tubular section 294 having a conductive
outer portion 294b and an inner tubular portion 294a formed of a varistor material,
the voltage and current operating characteristics of tubular section 294 are significantly
different as compared to tubular sections 262, 264, 266, 268 that are formed solely
of MOV material.
[0061] As illustrated in FIG. 13, it is further contemplated that a tubular section 296,
having an inner portion 296a formed of a conductive material and an outer portion
296b formed of an MOV material, could also be provided.
[0062] In this respect, different materials will affect the voltage and current-carrying
capabilities of a tubular section. It is contemplated that a circuit protection device
10 as heretofore described may utilize tubular sections formed of like varistor material
or may include tubular sections formed of different materials.
[0063] FIG. 14 illustrates yet another embodiment of the present invention. FIG. 14 illustrates
a voltage sensitive assembly 352 comprised of cylindrical tubular sections 362, 364,
366, and 368. Tubular sections 362, 364, 366, and 368 all have like inner and outer
diameters, but the axial lengths of tubular sections 366, 368 are different from each
other and are different from tubular sections 362, 364. FIG. 14 illustrates how tubular
sections of different lengths can be utilized to form a voltage sensitive assembly
according to the present invention. As taught above with respect to voltage sensitive
assembly 252A, one or more tubular sections could be eliminated and replaced by a
tubular insulator to vary the operating characteristics of the voltage sensitive assembly
within a circuit protection device 10. As will be appreciated by those skilled in
the art, different elements from voltage sensitive assemblies disclosed in FIGS. 10-14
could be combined in accordance with the present invention.
[0064] 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.
1. A disposable voltage suppression device (10) for suppressing voltage surges in an
electrical circuit, said device comprised of:
a tubular casing (32) formed of an electrically insulating material;
a first conductive component (92) attached to a first end of said casing;
a second conductive component (94) attached to a second end of said casing;
a tubular voltage sensitive assembly (52, 252, 252A, 252B, 252C, 253) within said
tubular casing, said voltage sensitive assembly comprised of two or more tubular sections
(262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368), said voltage sensitive assembly
having a first surface (52a) and a second surface (52b) and a predetermined voltage
rating across said first and second surfaces, said voltage sensitive assembly increasing
in temperature as voltage applied across said first and second surfaces exceeds said
voltage rating;
a first terminal (64) electrically connected to said first surface (52a) of said voltage
sensitive assembly and to said first conductive component (92);
a thermal element (122) electrically connected to said second surface (52b) of said
voltage sensitive assembly, said thermal element being an electrically conductive
solid at room temperature and having a predetermined softening temperature;
a second terminal (74) electrically connected to said second conductive component
(94), said second terminal having a contact portion (82, 82a) in electrical connection
with said second surface (52b) of said voltage sensitive assembly, said voltage sensitive
assembly sensing the voltage drop between said first conductive element and said second
conductive element, said second terminal (74) being maintained in electrical contact
with said voltage sensitive assembly by said thermal element (122) and being biased
away therefrom, wherein said second terminal (74) moves away from electrical contact
with said voltage sensitive assembly and breaks said electrical current path if an
over-voltage condition sensed by said voltage sensitive assembly exceeds the voltage
rating of said voltage sensitive assembly and causes said voltage sensitive assembly
to heat said thermal element beyond its softening point; and
an arc shield (132) movable from a first position wherein said arc shield allows contact
between said contact portion (82, 82a) of said second terminal and said voltage sensitive
assembly (52) to a second position wherein said shield (132) is disposed between said
contact portion of said second terminal and said voltage sensitive assembly when said
second terminal moves from electrical contact with said voltage sensitive assembly.
2. A voltage suppression device as defined in claim 1, wherein said voltage sensitive
assembly (262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368) is comprised of a
plurality of tubular metal oxide varistors (MOVs).
3. A voltage suppression device for suppressing voltage surges in an electrical circuit,
said device comprised of:
a tubular casing (32) formed of an electrically insulating material;
a first conductive component (92) attached to a first end of said casing;
a second conductive component (94) attached to a second end of said casing;
two or more tubular sections (262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368),
each of said tubular sections 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 (64, 74) for electrically connecting said tubular sections between said
first conductive component (92) and said second conductive component (94);
a normally closed, thermal switch comprised of one end (82, 82a) of one of said terminals,
a surface (52b) of said tubular sections and a thermal element (122), said one end
of one of said terminals being maintained in electrical contact with said surfaces
of said tubular sections by said thermal element (122), said thermal switch being
electrically connected in series with said tubular sections between one of said conductive
components (94) and said tubular sections (262, 264, 266, 268, 284, 294, 296, 362,
364, 366, 368), said thermal switch being thermally coupled to said tubular sections
wherein said one of said terminals (74) moves from a normally closed position wherein
said one of said terminals is maintained in electrical contact with said surfaces
of said tubular sections to an open position wherein said one of said terminals moves
out of electrical contact with said surfaces of said tubular sections to form a gap
between said one of said terminals (74) and said tubular sections (262, 264, 266,
268, 284, 294, 296, 362, 364, 366, 368) when the temperature of said tubular sections
reaches a level causing said thermal element to soften;
said one of said terminals including a contact portion (82, 82a) and a second portion
that extends away from the contact portion;
a non-conductive barrier (132) operable to move into said gap when said one of said
terminals (74) moves to an open position, said barrier preventing line voltage surges
from arcing between said one of said terminals and said tubular sections;
the second portion of said one of said terminals extending over at least a portion
of the non-conductive barrier and bending toward the thermal element so that the contact
portion (82, 82a) is held by the thermal element until said thermal element begins
to soften; and
said non-conductive barrier (132) 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 soften.
4. A voltage suppression device as defined in claim 3, wherein said thermal switch is
comprised of a terminal (74) held in electrical contact with said tubular sections
(262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368) by said thermal element, said
terminal being biased away from said tubular sections.
5. A voltage suppression device as defined in claim 3 or 4, wherein said thermal element
(122) is a low melting temperature solder material.
6. A voltage suppression device as defined in any one of the claims 3 to 5, wherein said
tubular sections (262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368) are comprised
of a metal oxide varistor (MOV) material.
7. A voltage suppression device as defined in any one of the preceding claims, wherein
said tubular sections (262, 264, 266, 268, 284, 294) of said voltage sensitive assembly
are identically formed or have like dimensions.
8. A voltage suppression device as defined in any one of the preceding claims 1 to 6,
wherein said tubular sections (362, 364, 366, 368) of said voltage sensitive assembly
have different dimensions.
9. A voltage suppression device as defined in any one of the preceding claims, wherein
said tubular sections (262, 264, 266, 268, 294, 296, 362, 364, 366, 368) of said voltage
sensitive assembly are formed of the same material.
10. A voltage suppression device as defined in any one of the preceding claims, wherein
at least one of said tubular sections (294, 296) has an inner portion (294a, 294b)
and an outer portion (294b, 296b).
11. A voltage suppression device as defined in claim 10, wherein said inner portion (294a)
of at least one said tubular section (294) is formed of a metal oxide varistor material
and said outer portion (294b) is formed of an electrically conductive material, or
wherein said outer portion (296b) of at least one said tubular section (296) is formed
of a metal oxide varistor material and said inner portion (296a) is formed of an electrically
conductive material.
12. A voltage suppression device as defined in claim 10 or 11, wherein said inner portion
(294a, 294b) and said outer portion (294b, 296b) of said at least one tubular section
are both tubular in shape.
13. A voltage suppression device as defined in any one of the preceding claims, wherein
said tubular sections (262, 264, 266, 268, 284, 294, 296, 362, 364, 366, 368) are
disposed adjacent to and in contact with each other in said tubular casing (32).
14. A voltage suppression device as defined in any one of the preceding claims 1 to 12,
wherein said tubular sections (264, 268) are spaced apart from each other within said
tubular casing, wherein, in particular a non-conductive insulator (276) is disposed
between said spaced-apart tubular sections (264, 268).
15. A voltage suppression device according to any one of the claims 1, 2 and 7 to 14,
wherein the second terminal is formed of a spring metal having one end in electrical
connection with said second surface of said voltage sensitive assembly (262, 264,
266, 268, 284, 294, 296, 362, 364, 366, 368) and another end connected to said second
conductive component (94), said second terminal (74) being bent from a normal and
relaxed configuration to be maintained in contact with said voltage sensitive assembly
by said thermal element, said second terminal being inherently biased away from said
voltage sensitive assembly toward said normal and relaxed configuration; and
the second terminal (74) having a second portion, the second portion extending through
the path of the arc shield and blocking the movement of the arc shield (132) until
the thermal element reaches its softening point.