Internal arc management and ventilation for electrical equipment

[0018] Referring to FIG. 1, an electrical enclosure in the form of a switch gear cabinet 100 generally known in the art is shown having a breaker section 101 for containing circuit breakers or other electrical equipment, a bus section 102 for distributing power to the various electrical equipment, and a cable section 103 for accepting and distributing line power. The switch gear cabinet 100 or a section thereof may serve as a cabinet protecting

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-4various 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 101 so that each draw out breaker (FIG. 2) 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 102,103.

[0019] The configuration of this type of cabinet 100 reduces airflow and transfers heat from breaker to breaker vertically. For example, cool airflow Amin enters through bottom inlet vents 107 of the cabinet 100 and heats up to Amax as the airflow travels vertically towards and through upper exhaust vents 109. As airflow travels through compartment vents 11 la-11 Id of the respective breaker compartments 105a-105d, the airflow heat increases from Al in a first breaker compartment 105a, to A2 in a second compartment 105d, and so on, until the airflow exits the cabinet 100 through the respective upper exhaust vent 109.

(0020] This type of cabinet 100 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.

(0021J Referring also to FIG. 2, in our prior Schneider Electric application 13/452,145; filed April 20, 2012 (attorney docket CRC-0266); individual arc channels 120a120c arc 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 100. The draw out breakers 122a-122c are insertable in respective breaker compartments 105a-105c of the cabinet 100. However, in this arrangement the heat may still build up vertically to an undesirable level for upper breakers.

(0022] 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.

-5[0023] Referring to FIGs. 3 and 4, an exemplary configuration illustrates the backplane or back mold 108 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 300. The arc channels 120a-120c are in fluid communication with ventilation channels which include an inlet vent channel 130 and an exhaust channel 132.

[0024] The inlet vent channel 130 in this example is a single intake plenum that receives airflow Amin through the inlet vent 107, alter the airflow travels through a backflow valve 134. The backflow valve 134 (and/or other optional filters) prevents arc products from 10 exiting the cabinet 100 through the inlet vent 107. Similar to the inlet vent channel 130, the exhaust channel 132 in this example is an exhaust common plenum that receives airflow from all the arc channels 120a-120c. The airflow continues outside the cabinet 100 through the upper exhaust vent 109 and exits as Amax'. The exhaust channel 132 is positioned near the line side bus connections 142b for the circuit breaker (not shown in Fig, 3) and acts as a funnel for arc gas received from an exhaust end of the arc channels 120a-120c. As such, the exhaust channel 132 serves as a gas mixing plenum in which arc products produced in one or more of phases A-C can be accepted.

[0025] FIG. 4, a diagrammatic view of a draw out breaker 300 and the back mold 108 according to one aspect of the invention, shows the fixed barriers 140 of the back mold 108 20 in relation to cluster shields 308a-308c on the back of the breaker 300. The cluster shields, collectively 308, are parallelepiped structures which surround the line and load connectors, also sometimes called clusters, 302a-302c of the draw out circuit breaker 300 for each of the three phases A-C. When the breaker 300 is in an engaged position as seen in Fig. 4, 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 306 of the back mold 108. The cluster shields 308a-308c fit closely within fixed barriers 140 of the back mold 108 and the resulting overlapping barriers for each phase form the arc channels 120a120c which are vented through the top or exhaust channel 132 (Fig. 3) common to each

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-6phase A-C. As shown in FIG. 4, the fixed barriers 140 overlap the cluster shields 308 a-308 c by a length 0 and are separated from the cluster shields 308a-308c by a distance G such that the resulting arc channels 120a-1 20c have non-gas tight seals as shown by arrows 312b -312d.

[0026] 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 10 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 140 of the proper materials forming the arc channels and their attached exhaust channels, e.g., the plenum of exhaust channel 132, the present invention removes the need for clearing the arc by an active arc extinguishing device, as would be typical in the known art.

[0027] The fixed barriers 140 can be located between phases A-C, between any phase -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 20 and grounded surfaces of different potential, the fixed barriers 140 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 140 and cluster shields 308 provide mechanical and dielectric separation between phases A-C and prevent sustained direct phase-to-phase arcing in the direction Q (Fig. 3) 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 132 which serves as a common plenum and holding chamber for the arc plasma at the end of the arc attenuating length L.

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[0028] 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 100 over that of the chimney system of Fig. 2, without sacrificing self extinguishing behavior.

[0029] 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

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-7to FIG. 5, a draw out circuit breaker chassis 150 includes inlet vent channels 152a-152c corresponding to each one of phases A-C.

(0030] 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 150. For example, the inlet vent channels 152a-l52c 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 arc 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 150. A further benefit provided by PVC tubing is that the inlet vent channels 152a-152 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 phasecommon chimneys for the vertically stacked breakers, each breaker compartment can be separately vented while maintaining arc-interrupting functionality.

[0031] The breaker chassis 150 further includes exhaust channels 160a, 160b that direct the airflow externally of the draw out circuit breaker 150. A first exhaust channel 160b is a common channel that receives airflow from both phase A and phase C of the breaker chassis 150. A second exhaust channel 160a is a dedicated channel that receives airflow only from the corresponding phase B of the breaker chassis 150. To combine the airflow from phases A and C, two sections of PVC 162a, 162c arc coupled to a common section 164a between the breaker chassis 150 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. 4). In contrast, the first exhaust channel 160b includes a continuous section of PVC 162b that continues the exclusive arc channel 120b (Fig. 4) of phase B. The second exhaust channel 160a ends at its own exhaust point 166a.

[0032] The exhaust channels 160a, 160b are help fill for ducting breaker exhaust to eliminate the risk of bums 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

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-8present 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.

(0033] Referring to FIG. 6, PVC tubing is implemented to provide ventilation channels in a different configuration of electrical equipment, which includes a lower three pole three-phase chassis 200, for accommodating a three- pole breaker, and an upper six pole three-phase chassis 201, for accommodating a six pole three-phase breaker. The three-phase chassis 200 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 204 that is horizontally positioned and that is coupled to a common vertical exhaust vent channel 206.

[0034] The six pole three-phase chassis 201 includes six inlet vent channels 208a208f 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 210 that is horizontally positioned and that is coupled to the common vertical exhaust vent channel 206. Thus, airflow from both the three pole three-phase chassis 200 and the six pole three -phase chassis 201 is exhausted from the single common exhaust vent channel 206.

[0035] 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.

[0036] During regular operation, the inlet vent channels 208a-208f and the exhaust channels 210 and 204 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 210 and 204 are connected with the arc channels surrounding the conductors for passive attenuation of the arc and evacuation of the arc products.

[0037] Referring to FIG. 7, arc channels with fixed barriers are implemented in an electrical enclosure for molded case breakers, such as fixed circuit breakers. For example, a

-9three-phase circuit breaker 220 is enclosed within an electrical enclosure 222 with each phase Λ-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/or interrupt arcs. A complementary top piece (not shown) completes the enclosure 222 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 220 into a common exhaust channel 231 to provide a sufficient arc channel for each phase.

[003 8] The enclosure 222 is attached to three top conduits 226a-226c and one bottom conduit 228. Two right top conduits 226b, 226c accommodate power cables 229 that are 10 inserted within the enclosure 222 and are routed through arc channels of each phase A-C to connect to the breaker 220. The left top conduit 226a functions as an exhaust vent channel and the bottom conduit 228 functions as an inlet vent channel for cooling purposes.

[0039] 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 229 between the breaker 220 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 231 between the lower fixed barriers 224a, 224b and the upper fixed barriers 230a, 230b.

[0040] Referring Io FIGs. 8A and 8B, 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 240 (FIG. 8A) is generally similar to the enclosure 222 described above in reference to FIG. 7 except that it has a funnel shape. Fig. 8B is the complementary top piece or cover plate. Unlike Fig. 7, attached cabling and conduits are not shown.

[0041] Specifically, the enclosure 240 encloses a fixed circuit breaker 242 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

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-10246c, and a right sidewall 246d. The length L of the barriers 246a, 246b is determined to maintain separation between the arc channels 244a-244c a sufficient length away from conductor lugs 248 to adequately attenuate and/or interrupt potential arcs occurring at the conductor lugs 248 when the breaker 242 is in operation.

[0042] The enclosure 240 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 240. The funnel end has a top wall 251 with three apertures 252a-252c for coupling to respective conduits (not shown). Each of the apertures 252a-252c can receive 10 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 240.

[0043] The enclosure 240 also includes a cover plate 260 (FIG. 8B) that serves to enclose and form the geometry of the arc channels 244a-244c. The cover plate 260 has fastening holes 262 for attachment, for example, to the sidewalls 246a, 246d, 250a, 250b and/or the barriers 246c, 246d. The cover plate 260 is removable to provide interior access to the enclosure 240. Although not shown for clarity purposes, a similar cover plate would be provided for the enclosure 222 of FIG. 7.

[0044] 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. 7 showing conductor joints in the form of lugs 225a-225c that connect respective cables 229 to the breaker 220).

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- 10a[0045] The arc channels and connected exhaust channels are helpful in passively attenuating and/or 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 (16.66 milliseconds for 60 hertz). Based on industry tests that commonly allow a total test duration of 500 milliseconds or more, the reduction in duration is significant (by a factor of about 50) because it reduces the amount of plasma generated, the overall burn risk, and the amount of damage to electrical equipment.

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- 11 [0046] While particular embodiments, aspects, and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing description without departing from the spirit and scope of the invention as defined in the appended claims.