Patent Document

BACKGROUND 
     1. Field 
     The disclosed concept relates generally to surge protection devices, and in particular to a surge protection apparatus having multiple surge protections devices and a display which indicates which one of the surge protections devices, if any, has experienced a failure. 
     2. Background Information 
     Electrical systems, such as electrical power distribution systems, periodically experience over-voltage conditions, such as transient over-voltage conditions, also called “surges.” Over-voltage conditions are problematic to electrical systems because they may cause damage to the loads, such as electronic devices or other hardware, that are coupled thereto. As a result, surge protection devices (SPDs) have been developed to protect the loads from over-voltages that would otherwise damage the loads. SPDs typically provide such protection by coupling various types of known transient-suppressing elements between the phase, and neutral and/or ground conductors of an electrical power distribution system. 
     As is known in the art, transient-suppressing elements, such as metal-oxide varistors (MOVs), silicon avalanche diodes (SADs) and gas discharge tubes (GDTs), typically assume a high impedance state under normal operating voltages. When the voltage across a transient-suppressing element exceeds a predetermined threshold rating, however, the impedance of the element drops dramatically, essentially short-circuiting the electrical conductors and “shunting” the current associated with the over-voltage through the transient-suppressing element and away from the load. 
     MOVs are probably the most commonly used transient-suppressing element. An MOV consists of two plates separated by an insulator, such as a metal oxide, that has a known voltage breakdown characteristic. When the voltage between the two plates reaches a certain level (the voltage breakdown level), the insulator breaks down and conducts current. MOVs, however, have operational limitations that must be taken into account when designing an SPD. Specifically, all MOVs have a maximum surge current rating that, if exceeded, may cause the MOV to fail. An MOV may also fail if subjected to repeated operation, even if the maximum transient current rating is never exceeded. The number of repeated operations necessary to cause failure is a function of the magnitude of the transient current conducted by the MOV during each operation: the lower the magnitude, the greater the number of operations necessary to cause failure. 
     In light of these limitations, prior art SPDs have been developed that use multiple MOVs in a parallel combination such that the MOVs share the total transient current. Each individual MOV in such a configuration only conducts a portion of the total transient current, making it less likely that any individual MOV will exceed its maximum transient current capacity. In addition, an SPD that uses a plurality of parallel MOVs can withstand a greater number of operations because of the lower magnitude of transient current conducted by each individual MOV. If internally fused and sorted by V/I characteristics, a parallel combination of MOVs is advantageous because the failure of any individual MOV will not cause a complete loss of SPD functionality. 
     There is room for improvement in the field of SPDs. 
     SUMMARY 
     In one embodiment, a surge protection apparatus is provided that includes a first surge protection device having a number of first transient suppressing elements, a second surge protection device having a number of second transient suppressing elements, and an I/O circuit coupled to the first surge protection device and the second surge protection device. The circuit has a number of display elements, wherein the circuit is structured and configured to receive input signals from the first surge protection device and the second surge protection device and (i) responsive to any one of the first transient suppressing elements failing, causes the number of display elements to provide a first indication indicating that at least one of the first transient suppressing elements has failed, and (ii) responsive to any one of the second transient suppressing elements failing, cause the number of display elements to provide a second indication indicating that at least one of the second transient suppressing elements has failed. In another embodiment, a method of indicating failures in a surge protection apparatus having a first surge protection device having a number of first transient suppressing elements, and a second surge protection device having a number of second transient suppressing elements. The method includes receiving input signals from the first surge protection device and the second surge protection device, responsive to the input signals indicating that any one of the first transient suppressing elements has failed, providing a first visual indication indicating that at least one of the first transient suppressing elements has failed, and responsive to the input signals indicating that any one of the second transient suppressing elements has failed, providing a second visual indication indicating that at least one of the second transient suppressing elements has failed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of an electrical system according to an exemplary embodiment of the disclosed concept; and 
         FIG. 2  is a schematic diagram of dual surge protection device according to one exemplary embodiment of the disclosed concept. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     As employed herein, the term “fastener” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts. 
     As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. 
     As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
       FIG. 1  is a schematic diagram of an electrical system  2  according to an exemplary embodiment of the disclosed concept. As seen in  FIG. 1 , electrical system  2  includes a power source  4 , which may be, for example and without limitation, a single phase or three phase AC electrical distribution system. Electrical system  2  further includes a load  6 , such as an electronic device or other hardware. In addition, to protect load  6  from over-voltages that might otherwise damage load  6 , electrical system  2  includes a dual surge protection device  8 . Dual surge protection device  8  is described in greater detail herein and provides such protection by coupling a number of transient-suppressing elements in parallel with load  6  between power source  4  and the neutral and/or ground (the illustrated embodiment) conductors of power source  4 . 
     According to one aspect of the disclosed concept, dual surge protection device  8  enhances performance by providing a higher current rating than would normally be possible. Dual surge protection device  8  provides this enhanced performance by including two surge protection devices therein that are connected in parallel with one another. As a result, dual surge protection device  8  is able to provide increased current protection as compared to a single surge protection device (e.g., two times the rating; 800,000 amps as opposed to 400,000 amps). 
       FIG. 2  is a schematic diagram of dual surge protection device  8  according to one exemplary embodiment of the disclosed concept. As seen in  FIG. 2 , dual surge protection device  8  includes a first surge protection device  10  and a second surge protection device  12 . First surge protection device  10  and second surge protection device  12  each include a number of transient-suppressing elements that are provided in parallel with load  6  between power source  4  and ground. In the exemplary embodiment, first surge protection device  10  and second surge protection device  12  each include a number of MOVs as the transient-suppressing elements. It will be understood, however, that alternative transient-suppressing elements, such as silicon avalanche diodes (SADs) or gas tubes, may also be used. In the illustrated exemplary embodiment (wherein power source  4  is a three-phase AC source), surge protection device  10  and second surge protection device  12  each include four groups of MOVs  14 , with each group  14  including one or more (e.g., four) MOVs and being associated with a particular phase/line of power source  4  (e.g., Phase A, Phase B, Phase C and Neutral). The MOV groups  14  are shown schematically in  FIG. 2  and labeled with reference numbers  14 A- 14 H. 
     In addition, surge protection device  10  includes a number of outputs  16 , labeled  16 A- 16 D, with each output  16  being associated with a respective one of the MOV groups  14 A- 14 D. Surge protection device  10  is structured, using, for example, a number of transistor devices (e.g., FETs), such that, when configured as shown in  FIG. 2 , each output  16  will have one of the following two states: (i) 0.5V if all of the MOVs in the associated MOV group  14  are fully operational, and (ii) 0.0V if any (i.e., one or more) of the MOVs in the associated MOV group  14  has failed (e.g., due to the occurrence of a surge condition). Similarly, surge protection device  12  also includes a number of outputs  16 , with each output  16  being associated with a respective one of the MOV groups  14 E- 14 H. Like surge protection device  10 , surge protection device  12  is structured such that, when configured as shown in  FIG. 2 , each output  16  will have one of the following two states: (i) 0.5V if all of the MOVs in the associated MOV group  14  are fully operational, and (ii) 0.0V if any (i.e., one or more) of the MOVs in the associated MOV group  14  has failed (e.g., due to the occurrence of a surge condition). The significance of this feature is described in detail below. 
     As seen in  FIG. 2 , dual surge protection device  8  further includes an I/O circuit  18 . As described below, I/O circuit  18  is configured to indicate which one of the surge protections devices  10  or  12 , if any, has experienced an MOV failure. 
     I/O circuit  18  in the exemplary embodiment includes eight comparators  20 , labeled  20 A- 20 H. The output of each of the comparators  20 A- 20 D is coupled to a first LED  22  for driving LED  22  described herein, and the output of each of the comparators  20 E- 20 H is coupled to a second LED  24  for driving LED  24  as described herein. 
     I/O circuit  18  also includes four first voltage dividers  26 , labeled  26 A- 26 D, and four second voltage dividers  28 , labeled  28 A- 28 D. In one non-limiting embodiment, each of the first voltage dividers  26  is a resistor. As seen in  FIG. 2 , outputs  16 A and  16 E are input into voltage divider  26 A, outputs  16 B and  16 F are input into voltage divider  26 B, outputs  16 C and  16 G are input into voltage divider  26 C, and outputs  16 D and  16 H are input into voltage divider  26 D. Voltage divider  26 A is coupled to the negative input of comparator  20 A and the negative input of comparator  20 E, voltage divider  26 B is coupled to the negative input of comparator  20 B and the negative input of comparator  20 F, voltage divider  26 C is coupled to the negative input of comparator  20 C and the negative input of comparator  20 G, and voltage divider  26 D is coupled to the negative input of comparator  20 D and the negative input of comparator  20 H. 
     As shown in  FIG. 2 , each voltage divider  28  has a 14 V input. Voltage divider  28 A is coupled to the positive input of comparator  20 A and the positive input of comparator  20 E, voltage divider  28 B is coupled to the positive input of comparator  20 B and the positive input of comparator  20 F, voltage divider  28 C is coupled to the positive input of comparator  20 C and the positive input of comparator  20 G, and voltage divider  28 D is coupled to the positive input of comparator  20 D and the positive input of comparator  20 H. 
     As a result of the above described configuration, the negative input of each comparator  20  will receive either 0.5V or 0.0V depending on the state of the associated output  16  and the associated MOV group  14 . In particular, if all of the MOVs in an MOV group  14  are fully operational, the state of the associated output  16  will be 0.5V and the negative input of the associated comparator  20  will receive 0.5V. If, however, any MOV in an MOV group  14  has failed, the state of the associated output  16  will be 0.0V and the negative input of the associated comparator  20  will receive 0.0V. Furthermore, the positive input of each comparator  20  will receive a constant 0.1 V (via the 14 V input and the associated voltage divider  28 ). 
     Moreover, the output of each comparator  20  will depend on the current state of the negative input thereof (as noted above, the positive input of each comparator  20  is at a constant 0.1V). In particular, if the negative input is 0.5V, the output of the comparator  20  will be low. If the negative input is 0.0V, the output of the comparator  20  will be high. Furthermore, if the output of any one of the comparators  20 A,  20 B,  20 C or  20 D is high, led  22  will be lit (otherwise LED  22  will not be lit). Similarly, if the output of any one of the comparators  20 E,  20 F,  20 G or  20 H is high, led  24  will be lit (otherwise LED  24  will not be lit). 
     Thus, in operation, if all MOVs in a surge protection devices  10  and  12  are operational, all of the outputs  16  of the surge protection device  10 ,  12  will be 0.5V and all of the negative inputs of the associated comparators  20  will be 0.5V. In this condition, both LED  22  and LED  24  will be off (unlit). If any of the MOVs in MOV groups  14 A,  14 B,  14 C or  14 D of surge protection device  10  fails, LED  22  will be turned on (lit), and if any of the MOVs in MOV groups  14 E,  14 F,  14 G or  14 H of surge protection device  12  fails, LED  24  will be will be turned on (lit). A lit LED  22  or  24  will indicate to an observer that the associated surge protection device  10  or  12  has had an MOV failure and therefore needs to be replaced. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.

Technology Category: 5