Abstract:
A device for diverting energy away from an arc flash occurring within an electrical power system is provided. The device comprising an arc source configured to create a second arc flash, a plasma gun configured and disposed to inject plasma in proximity of said arc source in response to the arc flash, an arc containment device configured and disposed to house said arc source and said plasma gun, said arc containment device comprising a cover configured and disposed to cover said arc source and said plasma gun, said cover comprising an inner surface and an outer surface, said inner surface being proximal to said arc source and said plasma gun, said inner surface including an insulative ceramic plasma spray coating.

Description:
BACKGROUND OF THE INVENTION 
     The embodiments described herein relate generally to power equipment protection devices and, more particularly, to apparatus for use in channeling exhaust gases and pressure away from a location of arc generation. 
     Known electric power circuits and switchgear generally have conductors that are separated by insulation, such as air, or gas or solid dielectrics. However, if the conductors are positioned too closely together, or if a voltage between the conductors exceeds the insulative properties of the insulation between the conductors, an arc can occur. The insulation between the conductors can become ionized, which makes the insulation conductive and enables formation of an arc flash. 
     An arc flash includes a rapid release of energy due to a fault between two phase conductors, between a phase conductor and a neutral conductor, or between a phase conductor and a ground point. Arc flash temperatures can reach or exceed 20,000° C., which can vaporize the conductors and adjacent equipment. Moreover, an arc flash can release significant energy in the form of heat, intense light, pressure waves, and/or sound waves, sufficient to damage the conductors and adjacent equipment. However, the current level of a fault that generates an arc flash is generally less than the current level of a short circuit, such that a circuit breaker may not trip or exhibits a delayed trip unless the circuit breaker is specifically designed to handle an arc fault condition. 
     Standard circuit protection devices, such as fuses and circuit breakers, generally do not react quickly enough to mitigate an arc flash. One known circuit protection device that exhibits a sufficiently rapid response is an electrical “crowbar,” which utilizes a mechanical and/or electro-mechanical process by intentionally creating an electrical “short circuit” to divert the electrical energy away from the arc flash point. Such an intentional short circuit fault is then cleared by tripping a fuse or a circuit breaker. However, the intentional short circuit fault created using a crowbar may allow significant levels of current to flow through adjacent electrical equipment, thereby still enabling damage to the equipment. 
     Another known circuit protection device that exhibits a sufficiently rapid response is an arc containment device, which creates a contained secondary arc to divert the electrical energy away from the arc flash point. For example, some known devices generate an arc, such as a secondary arc flash within an arc containment device or vessel, for use in dissipating energy associated with a primary arc flash detected on a circuit. At least some known arc containment devices include a metallic top or cover to withstand the high pressure, and extremely high temperature gases generated at the location where the arc is created. However, such containment devices can be damaged, or exhibit arc tracking to ground, due to the high temperature conductive gases and conductive residue generated within the device. During the secondary arc flash, hot ionized exhaust gases at high pressure are created. The exhaust gases exert significant thermal and mechanical stress on the cover. The high pressures generated within the arc containment device necessitate a strong robust material be used to form cover. However, while rigid covers, such as those formed from metal such as steel or aluminum, provide the necessary structural strength to withstand the high pressure in the arc containment device, the high temperature exhaust gases can cause damage to the metal, such as melting or burn-through. Other metals with higher melting temperatures, such for example as stainless steels, add increased costs and weight, and are therefore not desirable as cover materials. It is desirable to provide a coating that thermally insulates the cover from the high temperatures. Additionally, the ionized exhaust gases deposit soot or other conductive residue on cover that reduce resistance to arc tracking that may lead to a failure due to short circuit to ground, such as to a grounded frame. It is desirable to provide an arc containment device that is robust enough to withstand high pressure, resistant to high temperature, and of sufficiently high resistance to electrical tracking to isolate the top cover from ionized gases to protect against arc tracking failure, for example, to ground. 
     One known way to provide thermal protection to a metallic substrate is to apply a plasma spray thermal barrier coating to the metal. However, the compositions of conventional thermal barrier coatings as disclosed in the prior art have not additionally addressed the need for the desired increased arc tracking resistance to avoid ground strikes and low cost needed for the arc containment device 
     For at least the reasons stated above, a need exists for an arc containment device having an improved resistance to melting. Additionally, for at least the reasons stated above, a need exists for an arc containment device having an improved resistance to arc tracking. It would further be desirable for an improved device that is simple, robust, inexpensive, and without moving parts. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a device for diverting energy away from an arc flash occurring within an electrical power system is provided. The device comprises an arc source configured to create a second arc flash, a plasma gun configured and disposed to inject plasma in proximity of said arc source in response to the arc flash, an arc containment device configured and disposed to house said arc source and said plasma gun, said arc containment device comprising a cover configured and disposed to cover said arc source and said plasma gun, said cover comprising an inner surface and an outer surface, said inner surface being proximal to said arc source and said plasma gun, said inner surface including an insulative ceramic plasma spray coating. 
     In another aspect, a method of manufacturing a device is provided. The method includes an arc source configured to create a second arc flash, a plasma gun configured and disposed to inject plasma in proximity of said arc source in response to the arc flash, an arc containment device configured and disposed to enclose said arc source and said plasma gun, said arc containment device comprising a cover configured and disposed to cover said arc source and said plasma gun, said cover comprising an inner surface and an outer surface, said inner surface being proximal to said arc source and said plasma gun, said inner surface including an insulative ceramic plasma spray coating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an exemplary electronic equipment stack having a circuit protection system. 
         FIG. 2  is a perspective schematic diagram of an exemplary arc containment device that may be used with the circuit protection system shown in  FIG. 1 . 
         FIG. 3  is a cross-section schematic diagram of the arc containment device shown in  FIG. 2 . 
         FIG. 4  is a partially exploded diagram of the arc containment device shown in  FIG. 2 . 
         FIG. 5  is a perspective schematic diagram of the circuit protection system shown in  FIG. 1 . 
         FIG. 6  is a partially exploded view of the circuit protection system shown in  FIG. 1 . 
         FIG. 7  is a magnified partial cross section view of a portion of the arc containment device of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments of device and methods for use with a circuit protection system, wherein the high temperature and pressure of an arc flash are generated, are described herein. For example, the circuit protection system can receive a signal that indicates detection of a primary arc flash within a power system coupled to the circuit protection system. The circuit protection system can then generate a secondary arc flash within an arc containment device to transfer the energy generated by the primary arc flash away from the power system. The embodiments described herein enhance the performance of a circuit protection device when high temperature ionized gases and pressure are generated in the circuit protection device. 
       FIG. 1  is a front view of an exemplary electronic equipment stack  100  that is housed within an equipment enclosure  102 . Stack  100  includes one or more electronics modules  104  and a circuit protection system  106  that provides electronics modules  104  with protection from, for example, arc flash events. Enclosure  102  includes a plurality of compartments, including a lower compartment  108 , a center compartment  110  that houses circuit protection system  106 , and an upper compartment  112  that houses electronics modules  104 . Enclosure  102  has a top wall  114  that extends between a first side wall  116  of enclosure  102  and a second side wall  118 . An exhaust opening (not shown in  FIG. 1 ), such as a vent, extends through top wall  114  and is coupled in flow communication to an exhaust plenum (not shown in  FIG. 1 ). The exhaust plenum extends downward from top wall  114  behind electronics modules  102 , and into center compartment  110  where the exhaust plenum is positioned with respect to circuit protection system  106 . Notably, circuit protection system  106  includes an arc transfer device (not shown in  FIG. 1 ). The arc transfer device transfers energy away from a detected arc flash event in a circuit, such as electronics module  104  or a power feed. The arc transfer device may be an arc containment device, which is described in greater detail below. Alternatively, the arc transfer device may be a bolted fault device that transfers the energy associated with the arc flash event to another location to dissipate in any suitable manner. 
       FIG. 2  is a perspective schematic diagram of an exemplary arc containment device  200  that may be used with the circuit protection system  106  of  FIG. 1 ;  FIG. 3  is a cross-section schematic diagram of arc containment device  200 ; and  FIG. 4  is a partially exploded diagram of arc containment device  200 . In an exemplary embodiment, arc containment device  200  includes a top cover  202  ( FIGS. 2-6 ), an exhaust manifold  204  ( FIGS. 3 and 4 ), a shock shield  206  (shown in  FIGS. 3 and 4 ), and a conductor assembly  208  (shown in  FIG. 4 ). As shown in  FIGS. 2 ,  3 ,  5  and  6 , conductor assembly  208  includes a conductor base  210  and a conductor cover  212  with a plurality of electrical conductors (not shown) positioned therebetween. Each electrical conductor is coupled to an electrode support  214  that supports an arc source electrode  216  ( FIG. 4 ). Each arc source electrode  216  is rigidly mounted onto the conductor cover  212  and spaced apart to define an electrode gap  284  and thereby form an arc source  216 . Each electrical conductor (not shown) extends through conductor base  210  to connect the electrodes  216  to a power source (not shown), such as a power bus. The conductor base  210  and a conductor cover  212  may be made of any suitable electrically insulating material and composites to provide an electrically insulative support for the electrodes  216 . 
     An arc triggering device such as a plasma gun  282  is disposed proximate the gap  284 , for example centrally disposed with respect to the arc source electrodes  216 , and configured to ionize a portion of the space in the gap  284 . In one embodiment, the plasma gun  282  injects plasma as an arc mitigation technique, to create a secondary arcing fault in response a signal indicative of a primary arc flash within the power system coupled to the circuit protection system  106 . In an embodiment, the plasma gun  282  is covered by a plasma gun cover  218  ( FIG. 3 ). In operation, the arc source electrodes  216  generate an arc, such as a second arc flash, for use in dissipating energy associated with a primary arc flash detected on a circuit, thus producing high temperature exhaust gases and pressure within arc containment device  200 . 
     Conductor cover  212  includes a plurality of mounting apertures (not shown) that are each sized to receive a respective fastening mechanism therein to couple conductor cover  212  to a support such as a conductor base  210 . Moreover, conductor cover  212  includes an edge portion  220  having a plurality of recesses  222  formed therein ( FIG. 4 ). As will be discussed in more detail below, conductor cover  212  includes one or more mating features, such as a rib  229 , configured to mate with a corresponding mating feature, such as a slot  353  formed in an exhaust port member  345  of exhaust manifold  204 . 
     Top cover  202  includes a top surface  242 , a lip  244 , and a side surface  246  extending between top surface  242  and lip  244 . Lip  244  is sized to overlay exhaust manifold posts  232  ( FIGS. 2 and 4 ), and includes a plurality of mounting apertures  248  that are sized to receive a respective fastening mechanism  249 , such as a threaded bolt therein to couple to conductor cover  212 . For example, each mounting aperture  248  of top cover  202  aligns with a respective mounting aperture of exhaust manifold  204  and a respective mounting aperture  222  of conductor cover  212 . In operation, top cover is isolated from ground, such as frame  302 . In an embodiment, fastening mechanism  249  comprises a steel bolt, is coupled to the electrically insulating conductor cover  212 , to isolate the bolt  249  and cover  202  from the frame  302  ground. 
     Moreover, as shown in  FIGS. 3 and 4 , shock shield  206  is sized to cover electrodes  216  and is disposed over the electrodes  216  such that the arc source is contained within the shield  206 . In an embodiment shock shield  206  is fixedly coupled to a top surface  224  of conductor cover  212 . 
     In an exemplary embodiment, shock shield  206  includes a top surface  226  and a side surface  228 . A plurality of exhaust vents  230  are formed in top and side surfaces  226  and  228 . Exhaust manifold  204  is sized to cover shock shield  206 . Exhaust manifold  204  includes a plurality of posts  232  ( FIG. 4 ). Each post  232  includes a mounting aperture (not shown) sized to receive a respective fastening mechanism therein to couple exhaust manifold  204  to conductor cover  212 . Moreover, each post  232  is sized to fit within a respective recess  222  of conductor cover  212 . 
     In an exemplary embodiment, and as shown in  FIG. 3 , top cover  202  is sized to cover exhaust manifold  204  such that the manifold  204  is contained with cover  202  and to define a cavity  238  therebetween for use as a passageway or exhaust path  240 , generally indicated in  FIG. 3  by arrow “P”. In an exemplary embodiment, exhaust manifold  204  also includes a top surface  234  with a plurality of exhaust vents  236  extending therethrough and in flow communication with exhaust path  240 . Likewise, the plurality of exhaust vents  236  are in flow communication with the plurality of exhaust vents  230  of shock shield  206 . Additionally, exhaust manifold  204  includes at least one exhaust port member  345 . Exhaust port member  345  includes a first exhaust port surface  351  configured to cooperate with a portion of top cover  202  to define an opening or gap  358 . Gap  358  is disposed in flow communication with the exhaust path  240  and arranged to provide an exhaust port  350  for the venting of exhaust gases, heat, and pressure from cavity  238  and out of arc containment device  200 . In an exemplary embodiment, exhaust manifold  204  includes two exhaust port members  345  formed on the exterior of exhaust manifold  204 . In operation, the one or more mating features, such as a slot  353  disposed on exhaust port member  345 , cooperates with the corresponding mating features, such as rib  229 , disposed on conductor cover  212  to provide structural rigidity, and prevent undesired “blow-by” of the high temperature exhaust gases under high pressure from within exhaust manifold  204  to an electrical ground, such as the frame  302 , and thereby prevent an undesired ground strike. 
     Furthermore, arc containment device  200  includes one or more non-conductive exhaust ducts  322  positioned on the periphery of top cover  202 . In an exemplary embodiment, as illustrated in  FIGS. 4-6 , arc containment device  200  includes a two exhaust ducts  322 . Each exhaust duct  322  directs exhaust gases from exhaust ports  350   
       FIG. 5  is a perspective schematic diagram of circuit protection system  106 , and  FIG. 6  is a partially exploded view of circuit protection system  106 . In an exemplary embodiment, circuit protection system  106  includes a controller  300  and arc containment device  200 . The frame  302  is sized to support arc containment device  200  within equipment enclosure  102  ( FIG. 1 ). Preferably, frame  302  is electrically coupled to ground. Controller  300  is coupled to frame  302  to secure controller  300  to arc containment device  200  when inserting or removing circuit protection system  106  from equipment enclosure  102 . In an exemplary embodiment, frame  302  includes a bottom wall  304 , a first sidewall  306 , and a second side wall  308 . Side walls  306  and  308  each include one or more rollers  310  that are sized to be inserted into or used with racking rails (not shown) provided within an enclosure compartment, such as center compartment  110  ( FIG. 1 ). 
     During operation, controller  300  receives a signal from, for example, electronics modules  104  ( FIG. 1 ), indicating detection of a primary arc flash on a circuit that is monitored by one or more monitoring devices (not shown), such as a current sensor, a voltage sensor, and the like. In response to the detection, controller  300  causes a plasma gun  282  to emit a plume of an ablative plasma. Specifically, the plasma gun  282  emits the plasma into the gap  284  defined between electrodes  216  ( FIG. 4 ). The plasma lowers an impedance between the tips of electrodes  216  to enable formation of a secondary arc flash. The secondary arc flash releases energy including heat, pressure, light, and/or sound. 
     The secondary arc flash also results in high temperature ionized exhaust gases. The exhaust gases are channeled through exhaust vents  230  of shock shield  206 . The exhaust gases are also channeled through exhaust vents  236  ( FIG. 4 ) of exhaust manifold  204 , and into exhaust path  240  ( FIG. 2 ) defined between exhaust manifold  204  and top cover  202 . The exhaust gases flow along exhaust path  240  and are channeled in a first direction through exhaust ports  350  and then channeled in a second direction through exhaust duct  322 , and out of arc containment device  200  such as into an exhaust plenum (not shown in  FIGS. 5 and 6 ) within equipment enclosure  102 . For example, in an embodiment as illustrated in  FIG. 6 , the second direction may be in the same direction as the first direction. In another embodiment as indicated in  FIG. 6   a , the second direction may be at an angle to the first direction. For example in an embodiment, the second direction may be substantially horizontal when the first direction is substantially vertical. In another embodiment, the second direction may substantially horizontal when the first direction is substantially vertical. 
     In an embodiment, cover  202  is formed from a suitable metal, such as steel or aluminum, and an insulative ceramic plasma spray coating is applied using conventional methods to reduce or limit the flow of heat through the coatings to the surface  360 , and to increase the resistance to arc tracking along the surface  360 . 
     In an embodiment, a plasma spray TBC may be used to provide the thermal protection, and arc tracking resistance, as well as low cost necessary for proper functioning of cover  202 . As depicted in  FIG. 7 , in an embodiment, coating  380  is preferably a two-layer coating having a primary base or bond coating  362  and a secondary top coating  372 . 
     In one embodiment, the primary bond coating  362  is plasma spray deposited using known techniques on the interior surface  360  of cover  202  to a thickness range of about 3-12 thousandths of an inch (0.003-0.012 in.). The primary bond coating  362  preferably includes an alloy, JCrAlY, comprising 20-24 wt. % Cr, 7-12 wt. % Al, 0-1.5 wt. % Y, where J is one of Ni, Co, and Fe. In another embodiment, the primary bond coating may include an alloy, Ni5Al and cobalt, the alloy comprising 0-35 wt. % Ni, 0-35 wt. % Co, 0-24 wt. % Cr, 4-12% Al, 0-1.5 wt. % Y. 
     The secondary top coating  372  is applied using conventional plasma spray techniques over the primary bond coating  362  to a thickness range of about 5-30 thousands of an inch (0.005-0.030 in.), and preferably to a range of about 10-20 thousandths of an inch (0.010-0.020 in). The secondary top coating  372  is an insulative ceramic coating and may be a dense vertically cracked (DVC) thermal barrier coating (TBC) having relatively low thermal conductivity. As an alternative to DVC, the secondary top coating  372  may include a porous microstructure, for example having about 5-20% porosity. Specifically, the secondary top coating  372  may comprise one of an yttria-stabilized zirconia (YSZ), magnesia-stabilized zirconia (MSZ), or alumina. In an embodiment, the secondary top coating  372  comprises 7-9 wt. % yttria, and zirconia. 
     While each exhaust duct  322  is shown in the Figures, by way of example and not limitation, as having a generally triangular cross-section, it is contemplated that each exhaust duct  322  may comprise a pipe, tube, or channel having any generally convenient cross-section. Each exhaust duct  322  may be oriented and arranged to direct the exhaust gases in any desired predetermined direction. Likewise, while the embodiments in the Figures, by way of example and not limitation, illustrate two exhaust ports  350 , it will be understood that any number of exhaust ports may be formed as described, and arranged in flow communication with the exhaust path  240 . Likewise, while the embodiments in the Figures, by way of example and not limitation, illustrate two exhaust ducts  322  connected in flow communication with corresponding exhaust ports  350 , it will be understood that any number of exhaust ducts  322  may be provided in an embodiment. In an embodiment, as shown in  FIG. 6 , each exhaust duct  322  includes a lower or first exhaust duct portion  326  and an upper or second exhaust duct portion  328  that is coupled to lower exhaust duct portion  326 . For example, lower exhaust duct portion  326  includes a lip  330  that extends at least partially along a periphery of a top end  332 . Lip  330  is sized to be inserted into a bottom end  334  of upper exhaust duct portion  328 . Lower exhaust duct portion  326  includes a flange  336  along at least a portion of a bottom end  338 . Flange  336  includes a plurality of mounting apertures  340  that are sized to receive a respective fastening mechanism therein to couple to top cover  202 . For example, each mounting aperture  340  of lower exhaust duct portion  326  aligns with a respective mounting aperture  248  of top cover  202  and a respective mounting aperture of exhaust manifold  204 . Similarly, upper exhaust duct portion  328  includes a flange  342  along at least a portion of a top end  344 . Flange  342  includes a plurality of mounting apertures  346  that are sized to receive a respective fastening mechanism therein to couple to top cover  202 . For example, each mounting aperture  346  of upper exhaust duct portion  328  aligns with a respective mounting aperture  348  of top cover  202 . Preferably, as shown in  FIGS. 4-6 , the distal end of upper exhaust duct portion  328  is configured with a protective mesh or screen  347  to prevent undesired entry of objects into the exhaust duct  322 . 
     While the embodiments in the Figures, by way of example and not limitation, illustrate each exhaust duct  322  being formed of two separate components, it will be understood, that in an embodiment, each exhaust duct  322  may be unitary, or as any desired number of components coupled together. 
     A plurality of first primary electrical connectors  312  are coupled to arc containment device  200  to electrically connect arc containment device  200  to a plurality of conductors (not shown) of a circuit (not shown) that is being monitored and/or protected by arc containment device  200 . Moreover, controller  300  ( FIG. 5 ) includes a first secondary electrical connector  314  that connects controller  300  to a second secondary connector (not shown) for use in performing diagnostics and/or plasma gun firing tests. A position indicator  316  is coupled to top cover  202  and is oriented to engage a switch (not shown) that is provided in a racking cassette (not shown) to indicate a position of arc containment device  200  within the racking cassette as described in greater detail below. For example, position indicator  316  includes a flange  318  having one or more mounting apertures  320  extending therethrough and sized to receive a respective fastening mechanism to couple position indicator  316  to top cover  202 . Accordingly, top cover  202  includes one or more corresponding mounting apertures (not shown) that are positioned beneath respective mounting apertures  320  of flange  318 . Notably, position indicator  316  may be coupled to any suitable portion of arc containment device  200  that enables the switch to indicate the position of arc containment device  200  within the racking cassette. 
     Exemplary embodiments of apparatus for use in devices for protection of power distribution equipment are described above in detail. The systems, methods, and apparatus are not limited to the specific embodiments described herein but, rather, operations of the methods and/or components of the system and/or apparatus may be utilized independently and separately from other operations and/or components described herein. Further, the described operations and/or components may also be defined in, or used in combination with, other systems, methods, and/or apparatus, and are not limited to practice with only the systems, methods, and storage media as described herein. 
     Although the present invention is described in connection with an exemplary circuit protection environment, embodiments of the invention are operational with numerous other general purpose or special purpose circuit protection environments or configurations. The circuit protection environment is not intended to suggest any limitation as to the scope of use or functionality of any aspect of the invention. Moreover, the circuit protection environment should not be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment. 
     The order of execution or performance of the operations in the embodiments of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention. 
     When introducing elements of aspects of the invention or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.