Patent Application
20080117555
This invention relates generally to reducing arcing in surge suppression devices.
Surge suppression units are used for protecting electrical equipment from electrical power surges. There are many different arrangements of electrical components that are used for providing surge suppression. Generally, during normal non-power surge conditions, the surge suppression components provide a high resistance path between a power line and a neutral or ground line. When a power surge event happens, the surge suppressor components start conducting, shorting the power surge to ground or to a neutral line and away from any electrical equipment connected to the power line.
During these surge conditions, the surge suppression components that provide the shorting path for the power surge, such as power diodes or varistors, become hot and can explode and/or electrically arc to other components in the surge suppression unit. These explosions and arcing can damage other electrical surge suppression circuitry, such as other diodes or varistors that might have otherwise been used to provide surge suppression during subsequent power surges.
To reduce the undesirable effects from explosions and arcing, fuses are located in series with the diodes or varistors. The fuses are designed to blow at a particular power level that disconnects the associated diode or varistor from the power line experiencing the power surge. These fuses unfortunately reduce the overall power surge capacity of the surge suppression unit. In other words, the surge suppressor only redirects a power surge until the fuse blows. Thus, using a smaller fuse rating to prevent the undesirable effects of arcing also has the possible negative effect of reducing the overall peak current capacity of the surge suppression unit.
In the accompanying drawings which form a part hereof, and wherein like numbers of reference refer to similar parts throughout:
The MOVs (varistors) 18 provide a high resistance path between the line connected to terminal 24 and the line connected to terminal 26. For instance, when a power surge occurs on a power line connected to terminal 24, one or more of the varistors 18 start conducting, redirecting the power surge away from electrical equipment (not shown) connected to the power line and either to a neutral line or ground line connected to terminal 26.
As also mentioned above, the power surge while being redirected to terminal 26 can cause the varistors 18 to heat up enough to start burning or blow up. The power surge can also create arcing between the conducting varistor 18 and other varistors 18 or create arcing between the conducting varistor 18 and the other electrical components 14 on circuit board 22. These fires, explosions, and arcing can damage the other varistors 18 and other electrical components 14, possibly to the extent of rendering the entire surge suppression unit 12 inoperable.
Referring to
In one embodiment, the anti-arcing separator walls 20 are made of a fire resistant fiber, plastic, ceramic or fiberglass insulating material, such as fiberglass based GP03. In another embodiment, the separator walls 20 may be made from a honeycombed plastic or fiberglass material. However, any material that has a high insulating factor can be used. The separator walls 20 in this embodiment have a height that extends over the top of each adjacent varistor and a width that extends along the entire width of each adjacent varistor 18 from a front end to a back end. In this embodiment, each separator 20 is approximately two inches tall, two inches wide and approximately ⅙th inch thick. Of course, the dimensions of the separators 20 can vary depending on the size of the adjacent varistors 18 and the amount of desired arc retardation.
The separator walls 20 allow a substantially open area around each one of the varistors 18 while at the same time isolating each varistor 18 from adjacent varistors and other electrical components 14. In one embodiment, this is preferred over other alternative anti-arcing arrangements and materials that might be tightly compacted or encased around each varistor 18. Tightly compacting materials around the varistors 18 could actually increase the negative effects from an explosion. For example, a material tightly encased around a varistor 18 may create more pressure around the varistor 189 during a power surge resulting in a larger explosion and the projection of additional shrapnel from encasing material. The separator walls 20 allow air to freely circulate around the varistors 18 thus mitigating pressure buildup and the resulting explosion.
In another embodiment, the separator walls 20 may also be located in front and behind each varistor 18. In this embodiment, each varistor 18 might be completely surrounded and contained by separator walls 20. This may include a first unitary piece of separator wall material that extends in front of all of the varistors 18 and a second unitary piece of separator wall material that extends behind all of the varistors 18. The separator walls 18 would still be located between the varistors 18 with the front ends abutting against the front separator and the back ends abutting against the back separator. Alternatively, there may be individual front and back separator walls for each varistor 18.
In one embodiment, an epoxy or fiberglass material 42 may be laid down in between the varistors 18. The separator walls 20 are then inserted into the wet epoxy to anchor the separators to the printed circuit board or against the sides of the varistors 18. The epoxy 42 may extend underneath all of the varistors 18 in between and around the wires 43 that extend from the bottom of the varistors 18 and connect the varistors 18 to the printed circuit board 22. Alternatively, the epoxy may be applied to the sides and in between the varistors 18. The epoxy 42 can be an electronic module potting epoxy with flame retardant. The epoxy 42 further retards arcing that may occur between the varistors 18 and the conductors 43 that connect the varistors 18 to the printed circuit board 22 while the separator walls 20 retard the arching between adjacent varistors 18.
In an alternative embodiment, separator walls 20 are compressively held in place by the adjacent varistors 18. The varistors 18 are spaced close enough together so that the separators 20 can be slid in between the varistors 18 and then held vertically upright on opposite sides by the adjacent varistors 18. Clips or slots in the printed circuit board 22 can also be used to hold the separators 20 upright.
Any combination of the separator walls 20 and epoxy 50 may also be used along with the sand 60. The sand 60 is simply poured into the opening formed by enclosure 16. The top cover 52 is then attached over the top of enclosure 16 to hold in the sand 60.
This is just one example of how the surge suppression units 12 can be arranged. In other embodiments, the enclosure 70 may only contain one surge suppression unit 12 or alternatively may contain multiple different sized suppression units. For example,
In this example, the smaller surge suppression unit 12 is coupled between a neutral terminal 78 via bus bar 84 and ground via bus bar 86. The larger suppression units 82 provide additional surge suppression protection between power line terminals 92 and 76 and neutral line terminal 78. Any one, or all, of the surge suppression units 82 and/or 12 can include any combination of the anti-arc separator walls 20, epoxy 50, and/or sand 60 described above. Thus, each of the surge suppression units is more resilient to arcing, fires, explosions, and general destruction during a power surge.
Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.
