Switchgear including a circuit breaker having a trip unit with an interface to a number of arc fault sensors |
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申请号 | EP13178133.8 | 申请日 | 2013-07-26 | 公开(公告)号 | EP2696460A1 | 公开(公告)日 | 2014-02-12 |
申请人 | Eaton Corporation; | 发明人 | Benke, James J.; | ||||
摘要 | Switchgear (2) includes a plurality of bus bars (4); and a plurality of circuit breakers (6). At least one of the circuit breakers includes a trip unit (8). The trip unit includes an interface (10) to at least one arc fault sensor (12) operatively associated with the switchgear. The trip unit is structured to trip at least one of a corresponding one of the at least one of the circuit breakers and a shorting switch (14) responsive to current flowing through the corresponding one of the at least one of the circuit breakers and an arc fault signal (16) from the at least one arc fault sensor. | ||||||
权利要求 | |||||||
说明书全文 | The disclosed concept pertains generally to switchgear including systems for eliminating arcing faults at components of electric power systems. The disclosed concept also pertains to medium voltage switchgear. Electric power systems incorporate switches for control and protection purposes. Distribution systems, which form part of the overall electric power system, include main and branch power buses and circuit breakers mounted in metal cabinets to form switchgear. Interruption of current flow in the buses of the distribution system by a circuit interrupter creates an arc as the contacts of the circuit interrupter open. These arcs caused by interruption are contained and extinguished in the normal course of operation of the circuit interrupter. Circuit interrupters, such as circuit breakers, employ an overcurrent trip unit for protecting electrical conductors from damage due to excessive electrical currents. For example, a microprocessor-based overcurrent trip unit employs adjustable tripping characteristics to continuously monitor the electrical current flowing through the circuit breaker and initiate a trip. Unintended arcing faults can occur within switchgear cabinets, such as between power buses, or between a power bus and a grounded metal component. Such arcing faults can produce high energy gases, which pose a threat to the structure and nearby personnel. This is especially true when maintenance is performed on or about live power circuits. Frequently, a worker inadvertently shorts out the power bus, thereby creating an arcing fault inside the enclosure. The resulting arc blast creates an extreme hazard and could cause injury or even death. This problem is exacerbated by the fact that the enclosure doors are typically open for maintenance. A common approach to protecting personnel from arcing faults in switchgear has been to design the metal enclosures to withstand the blast from the arcing fault. This has been done at great additional costs due to the heavy gauge metal used and numerous weld joints needed to prevent flying debris. Even with these precautions, the blast from an arcing fault inside the switchgear cannot be contained. Recently, methods have been developed to minimize the severity of the blast from an internal arcing fault. These methods include pressure sensing and light detection, which sense the arcing fault within the switchgear and cause a circuit breaker to trip before significant damage can result. The pressure sensing method is limited by the insensitivity of the pressure sensors. By the time cabinet pressure has risen to detectable levels, the arcing fault has already caused significant damage. In a medium voltage system, an internal arcing fault would occur somewhere inside of the switchgear enclosure, frequently, but certainly not limited to the point where the cables servicing the load are connected. In a low voltage system, such as, for example, a motor control center, an internal arcing fault could occur within the load center panelboard when, for example, servicing line panclboards. A bare live copper bus could inadvertently be shorted. Another example for both low and medium voltage systems would be the shorting of the conductors by rodents, snakes, or other animals or objects. In the low voltage system, the arcing fault could clear itself, by burning or ejecting the short, but it may take more than one-half cycle to do so, thereby causing significant damage and great risk of injury to workers even in one-half cycle of arcing. A medium voltage system would behave similar to the low voltage system; however, the medium voltage system would be less likely to be self-extinguishing. The crowbarring of the shorting switch will extinguish the arc. Once the arc is out, and if the short has been burned away or removed, then system power can be restored. It is known to employ a high-speed shorting switch to eliminate an arcing fault. Known arc elimination devices and systems produce a bolted fault across the power bus (e.g., phase-to-phase, such as two switches for three phases; phase-to-ground, such as three switches for three phases), in order to eliminate the arcing fault and prevent equipment damage and personnel injury due to arc blasts. It is also known to employ various types of crowbar switches for this purpose. The resulting short on the power bus causes an upstream circuit breaker to clear the bolted fault by removing power. See, for example, A known shorting switch electronic circuit has an option to trip an upstream circuit breaker in addition to a shorting switch by sensing both current flowing though a power bus and an arc flash or arc light associated with an arcing fault of, for example, the power bus. There is room for improvement in switchgear. These needs and others are met by embodiments of the disclosed concept, which provide an interface to a number of arcing fault sensors as part of a circuit breaker trip unit, along with the capability of the circuit breaker trip unit to trip a shorting switch and/or a corresponding circuit breaker in response to sensed current and the sensed arcing fault from the interface to the number of arcing fault sensors. In accordance with one aspect of the disclosed concept, switchgear comprises: a plurality of bus bars; and a plurality of circuit breakers, at least one of the circuit breakers comprising: a trip unit, wherein the trip unit comprises an interface to at least one arc fault sensor operatively associated with the switchgear, and wherein the trip unit is structured to trip at least one of a corresponding one of the at least one of the circuit breakers and a shorting switch responsive to current flowing through the corresponding one of the at least one of the circuit breakers and an arc fault signal from the at least one arc fault sensor. As another aspect of the disclosed concept, switchgear comprises: a plurality of bus bars; a shorting switch structured to short a number of the bus bars to ground or to each other; and a plurality of circuit breakers, at least one of the circuit breakers comprising: a trip unit, the trip unit comprises an interface to at least one arc fault sensor operatively associated with the switchgear, and the trip unit is structured to trip at least one of a corresponding one of the at least one of the circuit breakers and the shorting switch responsive to current flowing through the corresponding one of the at least one of the circuit breakers and an arc fault signal from the at least one arc fault sensor. As another aspect of the disclosed concept, medium voltage switchgear comprises: a plurality of bus bars; and a plurality of medium voltage circuit breakers, at least one of the medium voltage circuit breakers comprising: a plurality of conductors electrically interconnected with the plurality of bus bars, a plurality of current sensors, each of the current sensors being integral with a corresponding one of the conductors, and a trip unit, the trip unit comprises a first interface to at least one arc fault sensor operatively associated with the medium voltage switchgear and a second interface to the current sensors, and the trip unit is structured to trip at least one of a corresponding one of the at least one of the medium voltage circuit breakers and a shorting switch responsive to current flowing through the conductors and an arc fault signal from the at least one arc fault sensor. 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:
As employed herein, the term "number" shall mean one or an integer greater than one (i.e., a plurality). As employed herein, the term "electrical conductor" shall mean a wire (e.g., solid; stranded; insulated; non-insulated), a copper conductor, an aluminum conductor, a suitable metal conductor, or other suitable material or object that permits an electric current to flow easily. As employed herein, the term "trip unit" shall have its conventional meaning as employed with a circuit interrupter, such as a low voltage or medium voltage circuit breaker, and shall further mean an external protective relay, an integral protective relay or an integral relay as is conventionally employed with a medium voltage circuit breaker. As employed herein, the term "circuit breaker" shall have its conventional meaning as applied to a low voltage or medium voltage circuit breaker, and shall further mean a fixed circuit breaker, a fixed mounted circuit breaker, or a drawout circuit breaker. As employed herein, the term "draw out circuit breaker" shall have its conventional meaning as applied to a low voltage or medium voltage circuit breaker, and shall further mean a withdrawable breaker or withdrawable circuit breaker. As employed herein, the term "low voltage" shall mean any voltage that is less than about 1000 VRMS. As employed herein, the term "medium voltage" shall mean any voltage greater than a low voltage and in the range from about 1000 VRMS to about 38 kVRMS. As employed herein, the statement that two or more parts are "connected" or "coupled" together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are "attached" shall mean that the parts are joined together directly. Referring to Examples 1-20, below, describe various example configurations corresponding to As shown in Referring to Point sensors, such as 36, are a sensor that just senses one specific point or area of the switchgear 2. The point sensor 36 senses light and then analyzes it to see if it is associated with a bad arc. A point sensor employs a copper conductor 37, which can be electrically connected to the circuit breaker trip unit 8 through a secondary connector (not shown). Secondary connectors are conductors and mounting brackets located on the top of the draw out circuit breaker 34 in the switchgear 2. There is no known way to connect "fiber optic" cables in this manner. A fiber optic cable can only go from one point to another point. In contrast, a point sensor, such as 36, has the ability to connect up to the switchgear 2 and the secondary connectors (not shown) of the draw out circuit breakers 34 by the secondary harness 38 (best shown in The trip unit 8 of The integral protective relay provided by the trip unit 8 processes sensor inputs corresponding to current flowing through the corresponding circuit breaker 6, as is conventional through current sensors 39 ( Referring to The at least one arc fault sensor 12 of Referring again to The circuit breakers 6 of Further to Example 6, the trip unit 8 can trip only the shorting switch 14 (shown in phantom line drawing in Further to Example 6, the trip unit 8 can trip only the corresponding one of the circuit breakers 6 responsive to the current flowing therethrough and the arc fault signal 16 from a number of the arc fault sensors 12. Further to Example 6, the trip unit 8 can trip both of the shorting switch 14 (shown in phantom line drawing in In this example, the switchgear 2 of The personal protection sensor 12 mounts to a maintenance person when proximate (e.g., proximate the front) of the switchgear 2. The maintenance person connects the personal protection sensor 12 to the circuit breaker trip unit 8 corresponding to the circuit breaker 6 being maintained to add safety. Alternatively, the maintenance person connects to the circuit breaker trip unit 8 corresponding to the main circuit breaker 26 of The personal protection sensor 12 can be coupled to a person's clothing (e.g., shirt). This is intended to protect a person who walks into a room for the switchgear 2. For example, the person may step in front of the switchgear 2, work on it, change settings, check features, and check meters. During that whole time they are protected because the personal protection sensor 12 can send the arc fault signal 16 to trip the corresponding circuit breaker 6 and/or trip the high speed shorting switch 14. In this example, the switchgear 2 of If the circuit breaker 6 is a low voltage circuit breaker, then the trip unit 8 is a trip unit rather than an integral relay. For conventional medium voltage circuit breakers, rather than the term "trip unit", the corresponding term is conventionally referred to as an external protective relay or simply a protective relay, which is external to the conventional medium voltage circuit breaker. For the disclosed trip unit 8, the disclosed concept can employ an external protective relay in addition to the disclosed "integral protective relay" or "integral relay", which is part of the circuit breaker 6 instead of part of the switchgear 2. For convenience of reference herein, the term "trip unit" is employed in connection with a low voltage circuit breaker, and the term "integral protective relay" is employed in connection with a medium voltage circuit breaker. Otherwise, the disclosed concept can employ substantially the same device, a "trip unit", for a low voltage circuit breaker and an "integral protective relay" for a medium voltage circuit breaker. In this example, the switchgear 2 is low voltage switchgear 48 as shown in Alternatively, the single fiber optic cable 50 is just routed in an area of the switchgear 48 corresponding to the bus bars 4. The fiber optic cable 50 is then routed to the front of a main circuit breaker, such as 24 of In this example, the switchgear 2 of Arcing light is extremely bright and arises from burning plasma or super-heated molten metal. As a result, an arc inside of the srvitchgear 52 (e.g., generally hidden in relatively small sealed areas) can be seen outside of the switchgear 52, in front of the switchgear 52, and in different compartments (not shown) thereof. The arcing light will appear in small openings, behind bolted holes, and through seams of metal doors. The fiber optic cable 60 can be routed inside or outside of the switchgear 52 to provide protection. In most cases, it is routed inside of the switchgear 52 (e.g., a default configuration). However, it can be mounted outside the switchgear 52 in cases where a user upgrades old equipment and does not wish to crawl in the switchgear 52, drill holes, and add a number of arc fault sensors. In this example, the fiber optic cable 60 is routed "through the door" of the switchgear 52 to the circuit breaker integral relay (trip unit 8) corresponding to the main circuit breaker 58. Low voltage switchgear, as in Example 16, is traditionally mounted "through the door," which means that a circuit breaker can be seen outside of the switchgear 48 ( As an alternative to Example 17, as shown in This example is somewhat similar to Example 16, except that the switchgear is the medium voltage switchgear 66, the fiber optic cable 62 is routed "behind the door" to the circuit breaker 70, and the fiber optic cable 62 is disconnected to rack the circuit breaker 70 out of the switchgear 66. Referring to As an alternative to Example 19, the switchgear 72 can be medium voltage switchgear. In this example, the switchgear 84 is low voltage switchgear. Examples 22-27, below, describe various example configurations corresponding to Somewhat similar to Example 21, the switchgear 84 can be medium voltage switchgear. This example is similar to Example 16, except as applied to the switchgear 84 and shorting switch 88 of This example is similar to Example 17, except as applied to the switchgear 84 and shorting switch 88 of This example is similar to Example 18, except as applied to the switchgear 84 and shorting switch 88 of This example is similar to Example 19, except as applied to the switchgear 84 and shorting switch 88 of This example is similar to Example 20, except as applied to the switchgear 84 and shorting switch 88 of This example is similar to Example 15, except that the trip unit 110 includes integral current sensors 108. As shown in Examples 29 and 30, below, describe various example configurations corresponding to This example is similar to Example 20, except as applied to the switchgear 100 and integral current sensors 108 of This example is similar to Example 17, except as applied to the switchgear 100 and integral current sensors 108 of The disclosed concept employs the circuit breaker trip unit 8 (e.g., without limitation, a low voltage circuit breaker trip unit; a medium voltage circuit breaker protective relay) to provide arc sensing. This provides a relatively very low cost upgrade of a conventional trip unit with the disclosed interface 10 to a fiber optic cable or point sensor. This provides a complete arc protection system, which is much smaller than known arc protection systems. The disclosed concept supports low voltage and medium voltage circuit breakers and switchgear, and a wide range of arc fault sensors. As employed herein, one arc fault sensor or any suitable plurality of arc sensors can be employed. For example, more than one arc sensor output can be sent to the circuit breaker trip unit 8 of The trip unit 8 and the arc sensor interface 10 are integral to the circuit breaker 6 of 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. |