Patent Description:
The hazards of unexpected and/or uncontrolled arcing events, also called arc faults, in an electrical cabinet are well known and include potential damage to equipment and harm to personnel in the operating environment caused by arc flash and arc blast, hereinafter referred to for simplicity as arc blast. Both passive and active arc control means are known in the art. Passive means include directed venting of the arc blast energy and gasses out of the cabinet. Other passive means may include reinforcement of the cabinet structure in an effort to withstand the blast. Neither of the above passive methods limits fault duration or is easily retrofitable into existing switchgear cabinets. Active means usually include some form of sensing and a switching mechanism to control the current. Concerns with active means may include expense, nuisance trips, speed, and undetected system failures. Of course, the quicker the arc is controlled the less harm is likely to be done by the arcing event.

<CIT> is directed to a circuit breaker arc flash venting system. It discloses a switchgear assembly with a plurality of circuit breaker compartments each containing a circuit breaker. When an arc flash occurs in one of the circuit breaker compartments, arc flash gases from the arc flash pass through a vent in the rear wall of the circuit breaker compartment into a section bus compartment. The section bus compartment includes phase conductors separated by interphase barriers, which, when enclosed by a rear insulating barrier, form channels that receive the arc gases and direct them to a vent on the roof of the switchgear assembly.

<CIT> is directed to the cooling of terminal contacts of a withdrawable switch. In that document heat from the terminal contacts of each phase is removed by using internal and external fans as well as ducts forming convection channels to channel air to, and away from, the terminal contacts.

<CIT> is directed to a self-pressurized arc diverter which includes a vessel configured to enclose a fusible member disposed in a conductor and a pressure-activated arc diverter.

A quick, economical, passive mechanism for controlling and extinguishing arc events inside electrical cabinets would be welcome in the art. To that end, the present invention refers to an electrical apparatus for management of arc faults according to claim <NUM> and a method for limiting arc blast, extinguishing arcs, and ventilating conductors in an electrical enclosure according to claim <NUM>. Accordingly, in its various aspects and embodiments the present invention teaches and provides an arc management system having dielectric surrounds for the conductors, generally referred to herein as "arc channels," surrounding the likely arc sites within a cabinet, such as electrical connection or proximity points between or among conductors and equipment, and preferably for the electrical conductors of each phase. The arc channels are joined to exhaust channels, e.g., plenums, which act as chambers and form a geometry to hold the arc until it is extinguished. The arc channel and exhaust channel will lengthen the nascent arc and attenuate the current and temperature until the arc is extinguished.

Advantageous embodiments may include features of depending claims. In some embodiments, the arc channels and exhaust channels are tunnels preferably formed by case members having opposable barriers to form gas tight seals of individual parallelepiped or other polyhedral structures. In some embodiments, the arc channels and exhaust channels are boxes preferably formed by case members having overlapping barriers to form individual parallelepiped or other polyhedral structures with non-gas tight seals. Since the arc and exhaust channel structures can be considered as basically tubular, terminology common to curved surfaces may be used herein as an aid to explanation.

Because the exhaust channels according to the invention can be integrated into ventilation systems for the equipment, the operation of the enclosure can be cooler, resulting in better performance with less material expenditure. By combining arc management structure and ventilation structure, the benefits of both may be combined and utilized within the typically confined spaces of electrical enclosures. Thus several advantages may be provided by the arc management system including arc prevention by physical barrier to inadvertent entry of shorting conductors such as dropped tools or vermin; and arc channeling with extinguishing by the arc channels and exhaust channels which are sized, located and arranged so as to draw out and hold the arc thereby lessening its current and heat with attendant equipment and safety benefits.

In its various aspects the invention may provide a readily adaptable arc management and ventilation system with a passive arc attenuation for fixed breakers or draw out breakers in various mounting configurations and enclosures. By "breakers" the person having ordinary skill in the art will understand that various pieces of equipment such as safety switches, motor control units and the like; and well as electrical connection or proximity points of the conductors, can be safely accommodated and managed according to the present invention.

The foregoing and additional aspects and embodiments of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.

The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

Referring to <FIG>, an electrical enclosure in the form of a switch gear cabinet <NUM> generally known in the art is shown having a breaker section <NUM> for containing circuit breakers or other electrical equipment, a bus section <NUM> for distributing power to the various electrical equipment, and a cable section <NUM> for accepting and distributing line power. The switch gear cabinet <NUM> or a section thereof may serve as a cabinet protecting various parts of the electrical equipment or conductors from the outside environment as known in the art. As used herein, a "cabinet" may also be a protective enclosure within another larger cabinet in some instances. Several breaker compartments 105a-105d are stacked vertically in the breaker section <NUM> so that each draw out breaker (<FIG>) will have a structure for receiving its draw out chassis for moving the breaker in and out of contact with the electrical supply feeding from the other two sections <NUM>, <NUM>.

The configuration of this type of cabinet <NUM> reduces airflow and transfers heat from breaker to breaker vertically. For example, cool airflow Amin enters through bottom inlet vents <NUM> of the cabinet <NUM> and heats up to Amax as the airflow travels vertically towards and through upper exhaust vents <NUM>. As airflow travels through compartment vents 111a-111d of the respective breaker compartments 105a-105d, the airflow heat increases from A1 in a first breaker compartment 105a, to A2 in a second compartment 105d, and so on, until the airflow exits the cabinet <NUM> through the respective upper exhaust vent <NUM>.

This type of cabinet <NUM> could also use better arc management. Arcs may be prone to happen due to reduced spacing and barrier-less energized conductors. Heretofore, the electrical conductors of adjacent phases have generally lacked barriers that can help attenuate and/or interrupt arcs during an arc fault event.

Referring also to <FIG>, in our prior Schneider Electric application <CIT> (attorney docket CRC-<NUM>); individual arc channels 120a-120c are added in the back plane behind draw out breakers 122a-122c with a common chimney vent for each of the three phases to increase airflow and reduce heat build-up in the cabinet <NUM>. The draw out breakers 122a-122c are insertable in respective breaker compartments 105a-105c of the cabinet <NUM>. However, in this arrangement the heat may still build up vertically to an undesirable level for upper breakers.

It has been found that the arc resistance is directly proportional to arc length and arc resistance is inversely proportional to arc (channel) cross section. Here in the present invention, we take advantage of lengthening the arc rather than shrinking the cross sectional area, thus allowing us to increase arc resistance to the point the arc self extinguishes. The exhaust plenums of the present invention further allow the arc products to cool to a lower temperature before exiting the cabinet.

Referring to <FIG> and <FIG>, an exemplary configuration illustrates the backplane or back mold <NUM> of one draw out breaker compartment, e.g., 105a, implemented with arc channels 120a-120c, each of the arc channels 120a-120c corresponding to a respective electrical phase A-C for a draw out breaker <NUM>. The arc channels 120a-120c are in fluid communication with ventilation channels which include an inlet vent channel <NUM> and an exhaust channel <NUM>.

The inlet vent channel <NUM> in this example is a single intake plenum that receives airflow Amin through the inlet vent <NUM>, after the airflow travels through a backflow valve <NUM>. The backflow valve <NUM> (and/or other optional filters) prevents arc products from exiting the cabinet <NUM> through the inlet vent <NUM>. Similar to the inlet vent channel <NUM>, the exhaust channel <NUM> in this example is an exhaust common plenum that receives airflow from all the arc channels 120a-120c. The airflow continues outside the cabinet <NUM> through the upper exhaust vent <NUM> and exits as Amax'. The exhaust channel <NUM> is positioned near the line side bus connections 142b for the circuit breaker (not shown in <FIG>) and acts as a funnel for arc gas received from an exhaust end of the arc channels 120a-120c. As such, the exhaust channel <NUM> serves as a gas mixing plenum in which arc products produced in one or more of phases A-C can be accepted.

<FIG>, a diagrammatic view of a draw out breaker <NUM> and the back mold <NUM> according to one aspect of the invention, shows the fixed barriers <NUM> of the back mold <NUM> in relation to cluster shields 308a-308c on the back of the breaker <NUM>. The cluster shields, collectively <NUM>, are parallelepiped structures which surround the line and load connectors, also sometimes called clusters, 302a-302c of the draw out circuit breaker <NUM> for each of the three phases A-C. When the breaker <NUM> is in an "engaged" position as seen in <FIG>, the electrical connectors 302a-302c are engaged with respective bus connectors, collectively 142a and 142b for load and line connections respectively, attached to a back plane <NUM> of the back mold <NUM>. The cluster shields 308a - 308c fit closely within fixed barriers <NUM> of the back mold <NUM> and the resulting overlapping barriers for each phase form the arc channels 120a-120c which are vented through the "top" or exhaust channel <NUM> (<FIG>) common to each phase A-C. As shown in <FIG>, the fixed barriers <NUM> overlap the cluster shields <NUM> a-<NUM> c by a length O and are separated from the cluster shields <NUM> a-<NUM> c by a distance G such that the resulting arc channels <NUM> a-<NUM> c have non-gas tight seals as shown by arrows <NUM> b -<NUM> d.

If an arc does occur, the arc channels are designed to prevent the arc from being sustainable by drawing out the arc along a certain geometry including a cross sectional area and a sufficient length L from the energized contact to the exhaust channel. This geometry, aided by the sublimation of materials forming the arc channel and exhaust channels during the arc event, forms a negative energy balance forcing the arc to extinguish and not reignite. Certain thermoset polyesters, thermoplastics or vulcanized fiber materials may be used as required for the desired sublimation. Thus, it will be appreciated that with the fixed barriers <NUM> of the proper materials forming the arc channels and their attached exhaust channels, e.g., the plenum of exhaust channel <NUM>, the present invention removes the need for clearing the arc by an active arc extinguishing device, as would be typical in the known art.

The fixed barriers <NUM> can be located between phases A-C, between any phase A-C and ground, between line and load terminals (for devices such as circuit breakers, contactors, or switches), between power connectors or insulated cables, or lugs (for devices such as bus bars). By reduction or elimination of through-air exposure between energized and grounded surfaces of different potential, the fixed barriers <NUM> are designed to reduce the chance that a phase to ground or phase to phase arc occurs in the first place. The arc channels 120a - 120c formed by fixed barriers <NUM> and cluster shields <NUM> provide mechanical and dielectric separation between phases A-C and prevent sustained direct phase-to-phase arcing in the direction Q (<FIG>) along a shortest path between phases A-C. Instead, the arc gases are routed in a direction R, which is perpendicular to the shortest path in the direction Q, and are kept separated until the length L has been achieved to promote self-extinguishing behavior. The gases are allowed to mix in the exhaust channel <NUM> which serves as a common plenum and holding chamber for the arc plasma at the end of the arc attenuating length L.

Thus each phase in the breaker compartment is dielectrically segregated with arc channels to the extent necessary, the arc channels being joined to a common exhaust plenum, and provided with a cooling channel which does not increase the heat level to the breakers above. By providing each breaker compartment with its own venting and arc interruption channels, and by feeding intake air and exhausting each phase by common plenum, cooler operation can be had for the cabinet <NUM> over that of the chimney system of <FIG>, without sacrificing self extinguishing behavior.

As further discussed below, many variations of through ventilation using inlets, plenums, and exhausts, can be implemented in different types of circuit breakers, such as draw out breakers, fixed breakers, or plug-on breakers. The ventilation channels can lead into or from the front, back, bottom, top, or sides of the breakers. For example, referring also to <FIG>, a draw out circuit breaker chassis <NUM> includes inlet vent channels 152a-152c corresponding to each one of phases A-C.

The inlet vent channels 152a-152c can be made from dielectric Polyvinyl Chloride (PVC) tubing and are fine-tuned in accordance with specific design requirements of the breaker chassis <NUM>. For example, the inlet vent channels 152a-152c include a horizontal section 154a-154c with an elbow joint connecting to a vertical section 156a-156c. The shape and size of the inlet vent channels 152a-152c are helpful in receiving airflow from cooler areas of the electrical enclosure. Thus, without the inlet vent channels 152a-152c (shaped and sized in accordance with specific design requirements), the received airflow might consist of relatively higher-temperature airflow near the breaker chassis <NUM>. A further benefit provided by PVC tubing is that the inlet vent channels 152a-<NUM> can be retrofitted into existing electrical equipment without further modifications to the electrical equipment and/or the electrical enclosure, and ensuring that each breaker in an enclosure can be provided individual arc attenuation and ventilation apparatus. Thus, rather than phase-common chimneys for the vertically stacked breakers, each breaker compartment can be separately vented while maintaining arc-interrupting functionality.

The breaker chassis <NUM> further includes exhaust channels 160a, 160b that direct the airflow externally of the draw out circuit breaker <NUM>. A first exhaust channel 160b is a common channel that receives airflow from both phase A and phase C of the breaker chassis <NUM>. A second exhaust channel 160a is a dedicated channel that receives airflow only from the corresponding phase B of the breaker chassis <NUM>. To combine the airflow from phases A and C, two sections of PVC 162a, 162c are coupled to a common section 164a between the breaker chassis <NUM> and an exhaust point 166b. Each section 162a, 162c is connected to a respective arc channel of the breaker inside the closed back mold (<FIG>). In contrast, the second exhaust channel 160a includes a continuous section of PVC 162b that continues the exclusive arc channel 120b (<FIG>) of phase B. The second exhaust channel 160a ends at its own exhaust point 166a.

The exhaust channels 160a, 160b are helpful for ducting breaker exhaust to eliminate the risk of burns as well as reducing the potential for and/or interrupting arcs. Arc products, such as plasma, gases, combustion products, etc., that are exhausted through the exhaust channels 160a, 160b are expected to cool to an acceptable level after traveling a certain length through the exhaust channels 160a, 160b. Further, the exhaust channels of the present invention may be configured to capture breaker tripping exhaust, thereby providing protection which is not even covered by existing industry standards, such as the National Fire Protection Association (NFPA) standards or the Institute of Electrical and Electronics Engineers (IEEE) standards.

Referring to <FIG>, PVC tubing is implemented to provide ventilation channels in a different configuration of electrical equipment, which includes a lower three pole three-phase chassis <NUM>, for accommodating a three- pole breaker, and an upper six pole three-phase chassis <NUM>, for accommodating a six pole three-phase breaker. The three-phase chassis <NUM> includes three inlet vent channels 202a-202c corresponding to arc channels surrounding respective ones of phases A-C (only phases A and B shown). Airflow from the arc channels is led into a single exhaust channel <NUM> that is horizontally positioned and that is coupled to a common vertical exhaust vent channel <NUM>.

The six pole three-phase chassis <NUM> includes six inlet vent channels 208a-208f leading to arc channels surrounding respective ones of poles A-F (only poles A-E being shown). Airflow from the inlet vent channels 208a-208f is eventually let into a single exhaust channel <NUM> that is horizontally positioned and that is coupled to the common vertical exhaust vent channel <NUM>. Thus, airflow from both the three pole three-phase chassis <NUM> and the six pole three -phase chassis <NUM> is exhausted from the single common exhaust vent channel <NUM>.

As such, an electrical configuration can include any number of inlet and exhaust channels. According to the above example, the number of inlet and exhaust channels can be less than the number of phases. Furthermore, the tubing of the electrical configuration can include sublimating materials for the conduit, and might have any cross-sectional shape, e.g., round or rectangular.

During regular operation, the inlet vent channels 208a-208f and the exhaust channels <NUM> and <NUM> provide cooling airflows over enclosed electrical conductors (e.g., line side conductors and/or load side conductors of a circuit interrupting device). Under arcing conditions, the same inlet vent channels 202a-202c and 208a-208f and exhaust channel <NUM> and <NUM> are connected with the arc channels surrounding the conductors for passive attenuation of the arc and evacuation of the arc products.

Referring to <FIG>, arc channels with fixed barriers are implemented in an electrical enclosure for molded case breakers, such as fixed circuit breakers. For example, a three-phase circuit breaker <NUM> is enclosed within an electrical enclosure <NUM> with each phase A-C having its own arc channel 221a-221c. The arc channels 221a-221c are defined in part by enclosure sidewalls 223a, 223b and lower fixed barriers 224a, 224b, which separate phases A-C to attenuate and interrupt arcs. A complementary top piece (not shown) completes the enclosure <NUM> and seals the fixed barriers in a gas tight manner to form the arc channels. The lower fixed barriers 224a, 224b extend a distance L from the breaker <NUM> into a common exhaust channel <NUM> to provide a sufficient arc channel for each phase.

The enclosure <NUM> is attached to three top conduits 226a-226c and one bottom conduit <NUM>. Two right top conduits 226b, 226c accommodate power cables <NUM> that are inserted within the enclosure <NUM> and are routed through arc channels of each phase A-C to connect to the breaker <NUM>. The left top conduit 226a functions as an exhaust vent channel and the bottom conduit <NUM> functions as an inlet vent channel for cooling purposes.

Both the lower fixed barriers 224a, 224b, and the upper fixed barriers 230a, 230b provide anchor points for the complementary top piece (not shown) as well as a physical path for routing the cables <NUM> between the breaker <NUM> and the respective conduits 226b, 226c. However, in this example only the lower fixed barriers 224a, 224b form the arc channels around each phase (in combination with features of the complementary top piece). Gas mixing is allowed in the exhaust channel <NUM> between the lower fixed barriers 224a, 224b and the upper fixed barriers 230a, 230b.

Referring to <FIG>, arc channels with fixed barriers are implemented in an electrical enclosure that has a non-rectangular shape, e.g., a funnel shape. According to this embodiment, an electrical enclosure <NUM> (<FIG>) is generally similar to the enclosure <NUM> described above in reference to <FIG> except that it has a funnel shape. <FIG> is the complementary top piece or cover plate. Unlike <FIG>, attached cabling and conduits are not shown.

Specifically, the enclosure <NUM> encloses a fixed circuit breaker <NUM> near a bottom straight end and includes arc channels 244a-244c - one arc channel per phase. The arc channels 244a-244c are defined by a left sidewall 246a, a left barrier 246b, a right barrier 246c, and a right sidewall 246d. The length L of the barriers 246b, 246c is determined to maintain separation between the arc channels 244a-244c a sufficient length away from conductor lugs <NUM> to adequately attenuate and interrupt potential arcs occurring at the conductor lugs <NUM> when the breaker <NUM> is in operation.

The enclosure <NUM> further includes a top funnel end which has two outwardly tapered sidewalls 250a, 250b that provide additional internal space for the exhaust channel as well as accommodating routing of power cables (not shown) and exhaust of heated air within the enclosure <NUM>. The funnel end has a top wall <NUM> with three apertures 252a-252c for coupling to respective conduits (not shown). Each of the apertures 252a-252c can receive respective power cables through the coupled conduits. Alternatively, at least one of the apertures 252a-252c can be dedicated to function as an exhaust vent for allowing heated air to exit the enclosure <NUM>.

The enclosure <NUM> also includes a cover plate <NUM> (<FIG>) that serves to enclose and form the geometry of the arc channels 244a-244c. The cover plate <NUM> has fastening holes <NUM> for attachment, for example, to the sidewalls 246a, 246d, 250a, 250b and/or the barriers 246c, 246d. The cover plate <NUM> is removable to provide interior access to the enclosure <NUM>. Although not shown for clarity purposes, a similar cover plate would be provided for the enclosure <NUM> of <FIG>.

In general each embodiment of the present invention may have arc channels which are tubular dielectric barriers that surround electrical conductor joints, i.e. where the sections of conductor are joined to each other, at the circuit breakers and other components. According to the illustrated examples, the arc channels can be walled segments that extend from a bottom conductor area, where low heat airflow Amin is received, to an upper area, where a higher heat airflow Amax' is exhausted to a plenum or exhaust. The plenum can be common among multiple phases as long as it is distanced sufficiently from the conductor area by an arc channel. In other examples, the arc channels may be positioned only near conductor joints of the breakers (see, e.g., <FIG> showing conductor joints in the form of lugs 225a-225c that connect respective cables <NUM> to the breaker <NUM>).

The arc channels and connected exhaust channels are helpful in passively attenuating and interrupting arcs that may occur at one or more of the conductor joints. For example, a system according to the present invention can conceivably passively interrupt an arc in less than one current cycle (<NUM> milliseconds for <NUM> hertz). Based on industry tests that commonly allow a total test duration of <NUM> milliseconds or more, the reduction in duration is significant (by a factor of about <NUM>) because it reduces the amount of plasma generated, the overall burn risk, and the amount of damage to electrical equipment.

Claim 1:
An electrical apparatus for management of arc faults, the apparatus comprising:
an electrical enclosure (<NUM>, <NUM>, <NUM>, <NUM>);
electrical equipment within the enclosure and having one or more electrical phases (A, B, C) with respective electrical conductors;
dielectric arc channels (120a-120c, 221a-221c, 244a-244c) having fixed barriers (<NUM>, 224a, 224b, 246b, 246c), each arc channel (120a-120c, 221a-221c, 244a-244c) surrounding a respective one of the electrical conductors at a conductor joint (225a-225c) thereof and having a sufficient length (L) to attenuate an arc produced at the conductor j oint; and
an exhaust channel (<NUM>, 162a-162c, <NUM>, <NUM>, <NUM>) connected in fluid communication to each arc channel (120a-120c, 221a-221c, 244a-244c) at the end of its sufficient length (L);
wherein the fixed barriers (<NUM>, 224a, 224b, 246b, 246c) separate the electrical conductors of the one or more electrical phases to form at least part of each of the dielectric arc channels (120a-120c, 221a-221c, 244a-244c),
characterized in that during arcing conditions, the exhaust channel (<NUM>, 162a-162c, <NUM>, <NUM>, <NUM>) and the dielectric arc channels (120a-120c, 221a-221c, 244a-244c) are configured to lengthen the arc and attenuate its current and temperature until the arc is extinguished.