Patent Application
20120068806
A surge protective device, such as a varistor, may be used to protect a circuit against excessive transient voltages. When triggered by a sufficiently high voltage, a varistor, for example, shunts current created by the high voltage away from the circuit it protects. A varistor may be deployed within electronic devices or in a power distribution system (e.g., at the point where an electrical wire enters a building or throughout a building).
One type of surge protection device is a Metal Oxide Varistor (MOV). An MOV may include a ceramic mass of zinc oxide grains, in a matrix of other metal oxides, between two metal plates. The boundary between the grains forms a diode junction, and the operation of an MOV is similar to that of a reversed-biased diode. When a small voltage (e.g., less than the breakdown voltage of the MOV) is applied across the MOV, only a small current flows through the MOV, caused by reverse leakage through the diode junction. When a sufficiently large voltage (e.g., greater than the breakdown voltage of the MOV) is applied across the MOV, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and current is allowed to flow through the MOV. The result of this behavior is a highly nonlinear current-voltage characteristic, in which the MOV has a high impedance at low voltages and a low impedance at high voltages.
When conducting during a sufficiently-large voltage condition, however, the MOV may heat up significantly and fail catastrophically. To prevent such a catastrophic failure, a contact may be attached to the MOV such that the contact becomes unattached at a sufficiently high temperature. For example, the contact may be soldered to the MOV, in which case the solder may melt at a sufficiently high temperature and spring away from the MOV. As described in more detail below, the contact may also be attached to the MOV with other heat-reactive, conductive material that, for example, softens at a predetermined or a sufficiently high temperature.
For example, device 100 may be connected in parallel between a power line and a ground line, between a power line and a neutral line, between a neutral line and a ground line, or between a power line and another power line. Device 100 may include a metal-oxide varistor (MOV). During normal operating conditions (e.g., non-surge conditions), the impedance between contacts 104 may be extremely high with only a small current flowing between contacts 104 through device 100. When the voltage between contacts 104 exceeds a threshold (e.g., an over-voltage or surge condition), the impedance between contacts 104 (e.g., through the MOV) may be significantly reduced, allowing current to flow (e.g., be shunted) between contacts 104 through device 100. While shunting the current flow, the MOV within device 100 may heat up significantly, a condition that itself could lead to a dangerous failure condition (e.g., damage to the circuitry that device 100 is intended to protect). As discussed below, however, device 100 may prevent current from flowing through device 100 when the MOV reaches a high temperature. As further discussed below, device 100 may prevent arcing within device 100 in a reliable manner.
Base portion 110 may form one wall (e.g., the base) of enclosure 102 of device 100. In one embodiment, base portion 110 may be formed of molded plastic. Base portion may provide support for conductor 204, conductor 206, support structure 208, and/or MOV 202. Base portion 110 may include a first hole 224-1 and a second hole 224-2 (collectively “holes 224”). As shown with dot-dash lines in
MOV 202 may include a voltage-sensitive element that exhibits high impedance at low voltage and low impedance at high voltages. MOV 202 may include a ceramic mass of zinc oxide grains, in a matrix of other metal oxides, between two metal plates. As shown in
Front surface 222-1 and rear surface 222-2 may each be covered with a plate of conductive material (not shown), such as copper, aluminum, steel, or a conductive alloy. In this embodiment, current flowing through MOV 202 and heat generated by MOV 202 may be more evenly distributed. The plate or plates of conductive material may be mechanically attached to front surface 222-1, such as with a conductive alloy or adhesive (e.g., solder). In one embodiment, epoxy or polyvinylchloride (PVC) may cover MOV 202 and the plate or plates of conductive material (e.g., around the plate of conductive material on rear surface 222-2 of MOV 202). In this embodiment, the epoxy or PVC may suppress arcing from rear surface 222-2 to finger 230 or from one surface 222-x to the other surface 222-x of MOV 202.
Conductor 204 and conductor 206 are comprised of a conductive material, such as metal (e.g., copper, tinned copper, or steel). Conductor 204 includes one end that forms external contact 104-1, as shown in
Conductor 206 includes one end that forms external contact 104-2, as shown in
Support structure 208 may include a front wall 233-1, a rear wall 233-2, and two side walls. The walls of support structure 208 may form a well 232 for holding middle portion 228 of conductor 206. In
In one embodiment, well 232 may restrict movement of middle portion 228 in a rearward direction (defined by arrow 234) and a forward direction (defined by arrow 236). While middle portion 228 is held by support structure 208, finger portion 230 may move in the rearward direction 234. Such movement may occur when a force is applied in the rearward direction 234, for example. Finger portion 230 may include characteristics of a spring such that removal of the force will return finger 230 to a rest position shown in
In one embodiment, the rear facing side of support structure 208 may abut against front surface 222-1 of MOV 202. In this embodiment, support structure 208 may also aid in the placement of MOV 202 inside enclosure 102 of device 100. In yet another embodiment, support structure 208 may be omitted entirely and base portion 110 may provide full support for conductor 206.
Cover portion 108 may include a first guide rail 306-1 and a second guide rail 306-2 (collectively “guide rails 306”). Guide rails 306 may be formed of non-conductive material, such as plastic. Guide rails 306 may be glued to side walls 308-4 and 308-5 or may be integrally formed with cover portion 108. Guide rails 306 may help guide MOV 202 as cover portion 108 is placed over metal oxide varistor (MOV) 202. In this embodiment, the rear surface of guide rails 306 may come into contact with front surface 222-1 of MOV 202. Thus, MOV 202 may be securely situated between guide rails 306 and rear wall 308-2 of cover portion 108.
In one embodiment, guide rails 306 may extend to top wall 308-1 of cover portion 108 and/or to bottom surface 310 of cover portion 108. In another embodiment, guide rails 306 may extend to front wall 308-3 of cover portion 108, providing a slot in side walls 308-4 and 308-5 for MOV 202.
As mentioned above, bottom surface 310 of cover portion 108 may come into contact with the top surface of 312 of base portion 110 to form seam 112. Seam 112 may be ultrasonically welded or sealed so as to form an air-tight and/or fluid-tight seal between base portion 110 and cover portion 108. Seal 112 may be sealed using other methods, such as with glue, adhesive, or tape. An air-tight and/or fluid-tight seal 112 may prevent escape of a fluid, such as oil, from enclosure 102, as discussed in more detail below.
Adhesive 402 may be conductive to enhance the electrical contact between finger 230 and front surface 222-1. If adhesive 402 is not conductive, then finger 230 may physically and electrically contact front surface 222-1. Adhesive 402 may include heat-reactive material that loses its adhesive properties (e.g., softens) at a known or predetermined temperature. Adhesive 402 may be metal alloy (e.g. solder), an epoxy, or a polymer (e.g., a conductive polymer). Adhesive 402 may have a relatively low softening or melting temperature. In one embodiment, adhesive 402 is solder (e.g., silver, bismuth, indium, tin, lead, or an alloy of metals). While lead or lead alloys may be used, lead is banned in many countries. Adhesive 402 (e.g., solder) may be a solid at room temperature (e.g., approximately 25 degrees Celsius (° C.)), may be a solid up to 35° C., and may melt at approximately 70 to 140° C. (e.g., 90-95, 96-100, 101-105, 106-110 , 111-115, 116-120, 121-125, 126-130, 131-135, or 136-140° C.). In one embodiment, adhesive 402 may lose its adhesive properties (e.g., has a melting or softening temperature) at approximately 93, 98, 103, 108, 113, 118, 123, 128, 133, or 138° C.
Once finger portion 230 has separated from MOV 202, however, there is a danger that an electrical arc may form between finger portion 230 and MOV 202 (e.g., the gap between finger portion 230 and MOV 202). In one embodiment, enclosure 102 may be filled with a non-conductive fluid 502 (e.g., a liquid fluid), such as oil. In this embodiment, when adhesive 402 melts and finger portion 230 moves away from MOV 202, fluid 502 may flow into the space between finger portion 230 and MOV 202, as shown in
Fluid 502 may include many different types of oils, including mineral oil, vegetable oil, or seed oils. Fluid 502 may include dielectric insulating fluid, such as BIOTEMP®. Fluid 502 may include fire-resistant fluids, such as Envirotemp™ FR3. FR3 is a soy-based, non-silicone-based fluid. Fluid 502 may meet standards issued by one or more regulatory agencies or professional associations, such as the National Electrical Code (NEC), National Electric Safety Code (NESC), Underwriters Laboratories (UL), the Institute for Electrical and Electronics Engineers (IEEE), Occupational Safety and Health Administration (OSHA), and/or the European Agency for Safety and Health at Work, etc.
Placing fluid 502 in enclosure 102 may allow for device 100 to suppress arcing without moving an arc shield between finger portion 230 and MOV 202. Further, fluid 502 in enclosure 102 may allow for device 100 to suppress arcing without springs to move such an arc shield between finger portion 230 and MOV 202. Thus, placing fluid 502 in enclosure 102 may allow for suppression of an arc more reliably, e.g., without the additional points of failure introduced by an arc shield and springs to move the arc shield. Further, adding an arc shield and springs to move the arc shield may be labor intensive and complex. Thus, placing fluid 502 in enclosure 102 may be simpler than constructing a device 100 with an arc shield and additional springs. A simpler construction may reduce manufacturing costs. Further, a construction with fewer parts (e.g., no arc shield or additional springs) may also reduce manufacturing costs.
Fluid 502 may also promote the more even heating of MOV 202 and device 100. Thus, fluid 502 may prevent “hot spots” on MOV 202, which may, for example, lead to points of premature failure and possibly a catastrophic failure before the melting of adhesive 402. Fluid 502 may also control the rise of temperature of MOV 202, which may extend the life of the device 100 under normal operating conditions. Fluid 502 may also suppress arcing between rear surface 222-2 (or a conductive plate on rear surface 222-2) and finger portion 230 and/or rear surface 222-2 and front surface 222-1 (or conductive plates on surfaces 222). In this embodiment, fluid 502 may allow for the omission of shielding (e.g., PVC or epoxy) around MOV 202 and/or conductive plates on surfaces 222, thus reducing manufacturing time and cost. Further, finger portion 230 may be attached to front surface 222-1 of MOV 202 in places other than the center, such as the top right, the top left, the bottom right, or the bottom left of MOV 202. Attaching finger portion 230 to the top right of MOV 202 may allow for the elimination of middle portion 228 of conductor 206.
In one embodiment, conductor 204 may also be attached to rear surface 222-2 similarly to how conductor 206 is attached to front surface 222-1. In this embodiment, conductor 204 and/or conductor 206 may decouple MOV 202 from a circuit, depending on which conductor 204 or 206 heats up fastest. This configuration may also provide for a more reliable and predictable device. Further, in this embodiment, conductor 204 may be attached to the bottom left of rear surface 222-2 and conductor 206 may be attached to the top right of front surface 222-1; or conductor 204 may be attached to the top left of rear surface 222-2 and conductor 206 may be attached to the bottom right of front surface 222-1, for example.
In one embodiment, a third contact (not shown) may be attached to MOV 202 (e.g., to front surface 222-1) to indicate whether finger portion 230 has been disconnected from the protected circuit. For example, if the protected device is protected by an array of devices (such as device 100), a monitor may determine and be able to display the percentage of devices configured to protect the circuit (e.g., the number of de-coupled devices divided by the total number of devices). In one embodiment, a switch (e.g., a micro switch internal to enclosure 102) may flip from one position to another (e.g., from off to on or from on to off) when finger portion 230 moves from the position shown in
In one embodiment, enclosure 102 may include a plurality of MOVs. For example,
Although the invention has been described in detail above, it is expressly understood that it will be apparent to persons skilled in the relevant art that the invention may be modified without departing from the spirit of the invention. Various changes of form, design, or arrangement may be made to the invention without departing from the spirit and scope of the invention. Therefore, the above mentioned description is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined in the following claims.
Although embodiments above may use an MOV, other devices may be used. For example, any device may be used that has a highly nonlinear current-voltage characteristic, in which the device has a high impedance at low voltages and a low impedance at high voltages. In one embodiment, a gas discharge tube (GDT) may be used instead or in addition to an MOV. A GDT may conduct when the voltage between terminals exceeds a threshold. If a GDT continues to conduct, however, it may overheat, a condition that may cause a catastrophic failure. In this embodiment, the GDT may include conductors that decouple from the GDT at a threshold temperature. The GDT may be surrounded by oil in an enclosure, as described above. In one embodiment, a GDT may be in the same enclosure as a MOV. In other embodiments, a silicon avalanche diode (SAD), a zener diode, a transient suppression diode, a quarter-wave coaxial surge arrestor, a Silicon carbide surge arrestor or varistor (SiCV), and/or a carbon block spark gap overvoltage suppressor may be used additionally or alternatively to an MOV or a GDT. Further still, various combinations of these different protection devices may be in the same enclosure, such as enclosure 602 (e.g., any GDT/MOV combination, any GDT/SAD combination, any MOV/SAD combination, and/or any MOV/SAD/GDT combination).
In one embodiment, conductors 204 and 206 may also act as a fuse. When current through conductor 206 exceeds a threshold, for example, conductor 206 may break. Fluid 502 may serve to suppress arcing across a gap formed at the break of conductor 206. Such a break of conductors 204 or 206 may also be a failure (e.g., unintended failure) condition. In this case, fluid 502 may also act to suppress arcing across a gap formed at the break of conductor 206. Fluid 502 may act to suppress arcing across any gap formed as a result of a failure of components of the surge protection device.
Further, any method of attaching/releasing finger portion 230 to/from the nonlinear device may be used. For example, any method may be used that releases finger portion 230 from the nonlinear device during a thermal and/or low impedance condition.
For example, although one embodiment may include oil in enclosure 102 without the additional components of an arc shield and springs to move the arc shield, alternative embodiments may include these components in addition to oil in enclosure 102. As another example, while a liquid is contemplated for fluid 502, fluid 502 may include a gas to suppress arcing. In one embodiment, fluid 502 is entirely a gas.
Although terms such as “front,” “rear,” “forward,” “backward,” “top,” “bottom,” “left,” and “right” are used, these terms are used for convenience to show elements in the figures relative to each other. These terms are not used to indicate absolute direction or position. As such, the terms “rear” and “front” may be interchanged, “top” and “bottom” may interchanged, etc.
No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
This patent application claims priority to U.S. Provisional Application No. 61/385,235, filed Sep. 22, 2010, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61385235 | Sep 2010 | US |
