Abstract:
A surge suppression unit includes a circuit board containing electrical surge suppression components configured to redirect power surges. Anti-arcing separator walls are vertically aligned in between at least some of the electrical components for reducing electrical arcing. An epoxy may be spread in between the surge suppression components to both hold the separator walls upright while at the same time further retarding arcing. In another embodiment, the epoxy can be spread over substantially an entire top surface of the printed circuit board covering substantially all low profile electrical components while leaving a large portion of other higher profile MOVs or SADs uncovered. In yet another embodiment, the electrical components can also be covered with a fire retardant sand.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates generally to reducing arcing in surge suppression devices. 
       BACKGROUND 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    In the accompanying drawings which form a part hereof, and wherein like numbers of reference refer to similar parts throughout: 
           [0006]      FIG. 1  is a perspective view of a surge suppression unit with improved arc resistance. 
           [0007]      FIG. 2  is a circuit diagram for the surge suppression unit shown in  FIG. 1 . 
           [0008]      FIG. 3  is a side sectional view of the surge suppression unit shown in  FIG. 1 . 
           [0009]      FIG. 4  is a top view of another embodiment of the surge suppression unit that includes epoxy covering a printed circuit board. 
           [0010]      FIG. 5  is a side sectional view of the surge suppression unit shown in  FIG. 4 . 
           [0011]      FIG. 6  is a side sectional view of another embodiment of the surge suppression unit that contains a fire retardant sand. 
           [0012]      FIG. 7  is a perspective cut-away view of two of the surge suppression units stacked in an enclosure. 
           [0013]      FIG. 8  is a perspective cut-away view of another surge suppression system that includes different sized surge suppressor units. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  shows a surge suppression unit  12  that includes multiple Metal Oxide Varistors (MOVs)  18  connected to a printed circuit board  22 . Other electrical circuitry and components  14  are also connected to the circuit board  22 . A power line or neutral line (not shown) is connected to a first terminal  24  and a ground line or neutral line (not shown) is connected to a second terminal  26 . The circuit board  22 , varistors  18  and other electrical components  14  are all contained within an enclosure  16 . The enclosure  16  includes front and back walls  16 A and  16 B, respectively, and side walls  16 C. A top cover  52  attaches over walls  16 A- 16 C. 
         [0015]    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 . 
         [0016]    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. 
         [0017]      FIG. 2  shows one example of a circuit diagram for the surge suppression unit  12  shown in  FIG. 1 . The terminal  24  is connected through conductor  30  to each of the varistors  18  via associated fuses  28 . The opposite end of each varistor  18  is connected through conductor  32  to the terminal  26 . A power sensing line  34  is connected to each varistor  18  through resistors  36 .  FIG. 3  shows a side sectional view of the surge suppression unit  12  shown in  FIG. 1 . 
         [0018]    Referring to  FIGS. 1-3 , to reduce the effects of fires, explosions and arcing, separator or spacer walls  20  extend vertically up between the adjacent varistors  18 . The separator walls  20  impede arcing paths between the conducting varistor  18  and other varistors  18 , and also impede any arcing paths between the conducting varistor  18  and the other electrical components  14 . 
         [0019]    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 ⅙ th  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. 
         [0020]      FIG. 2  shows a separator wall  20 A located between varistors  18 A and  18 B and separator wall  20 B located between varistors  18 B and  18 C. The separators  20 A and  20 B prevent an electrical power surge that is conducted through one of the varistors  18 B, for example, from arcing  40  to varistor  18 A or varistor  18 C. This allows the surge suppression unit  12  to withstand multiple power surges while still providing suppression for subsequent power surges. The fuses  28  disconnect the power surge when the varistors  18  get too hot. Because, the varistors  18  are less likely to arc, the fuses  28  can, but are not required to, have higher current ratings. Thus, the surge suppression unit  12  may maintain a higher power surge rating while at the same time having increased resilience to power surges. 
         [0021]    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. 
         [0022]    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 . 
         [0023]    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 . 
         [0024]    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. 
         [0025]      FIG. 4  shows a top view of an alternative embodiment of the surge suppression unit  12 .  FIG. 5  shows a side sectional view of the surge suppression unit  12  shown in  FIG. 4 . In this embodiment, the epoxy  50  covers the entire top surface of the circuit board  22 . The epoxy  50  covers substantially all of the electrical components  14 , other than the varistors  18 , that are located on the top of the circuit board  22 . Some of the other larger profile electrical components  14  and  18  may only be partially covered with the epoxy  50 . The epoxy  50  may be made of a non-conductive resin, plastic, or fiberglass material that impedes arcing between the varistors  18  and the other electrical components  14  and conductors on printed circuit board  22 . The varistors  18  are not completely covered in epoxy  50 , to avoid possibly increasing the explosive effects that may result by completely encasing each varistor  18 . 
         [0026]      FIG. 6  shows yet another embodiment of the surge suppression unit  12  that contains sand  60  for retarding arcing and reducing the effects of explosions and fires. The porous sand and air existing between the sand granules prevent the same shrapnel effects that may result from encasing the varistors in denser insulating materials. A fire retardant material  62  may be combined with the sand  60  to further retard arcing and the effects of fires or explosions within the enclosure  16 . A similar material used in fire extinguishers, such as monoammonium phosphate may be used for fire retardant  62 . In one embodiment, a 50/50 mixture of sand  60  and fire retardant material  62  is used. Of course, other types of fire retardants  62  and fire retardant/sand ratios might also be used. Epoxy can also be spread over the sand  60  to keep it retained within enclosure  16 . 
         [0027]    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 . 
         [0028]      FIG. 7  shows two of the surge suppression units  12  stacked vertically on top of each other inside of an enclosure  70 . The two suppression units  12  are coupled together at a first end by a connector post  72  and at a second end by a connector post  74 . The connector post  72  electrically couples terminal  26  to a bus bar  78  that is coupled to neutral or ground. The post  74  electrically couples terminal  24  to a power line connector  76 . The MOVs  18  extend along substantially the entire length of the circuit board  22  and each is separated by one of the anti-arcing separator or divider walls  20 . 
         [0029]    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,  FIG. 8  shows a power surge protection assembly  80  that includes both larger sized suppression units  82  and smaller sized suppression units  12  connected side-by-side. The surge suppression units  82  may include similar power surge protection components at surge suppression units  12  previously described above in  FIGS. 1-7 . However, the larger sized surge suppression units  82  may include more surge suppression components, such as more MOVs  18 . 
         [0030]    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. 
         [0031]    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.