Patent Application
20130120879
1. Field
The disclosed concept pertains generally to arc flash arresters and, more particularly, to arc flash arresters, such as, for example, shorting switches or other devices that arrest or quench an arc flash or arcing fault. The disclosed concept also pertains to switchgear systems including an arc flash arrester.
2. Background Information
Switchgear typically includes a combination of an electrical busway and electrical disconnects, fuses and/or circuit breakers employed to electrically connect and disconnect electrical equipment. As one non-limiting example, switchgear includes an assembly of one or more motor starters that can also contain circuit breakers and fused switches. Example switchgear devices include, but are not limited by, a circuit interrupter, such as a circuit breaker (e.g., without limitation, low voltage; medium voltage; high voltage); a motor controller/starter; and/or any suitable device which carries or transfers current from one place to another.
Electric power systems incorporate switches for control and protection purposes. Distribution systems, which form part of an 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 breaker creates an arc as the contacts of the circuit breaker open. These arcs caused by interruption are contained and extinguished in the normal course of operation of the circuit breaker.
At times, however, 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 live panelboards. 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 a shorting switch will extinguish the arc. Once the arc is out, and if the short has been burned away or removed, then, after repairs are made, 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, U.S. Pat. Nos. 7,145,757; 7,035,068; 6,839,209; 6,724,604; 6,693,438; 6,657,150; and 6,633,009. As a result, system power is lost due to the tripping of the upstream circuit breaker.
Known prior medium voltage shorting switches employ vacuum interrupters or vacuum envelopes having a partial vacuum therein.
Known prior low voltage shorting switches employ air at atmospheric pressure as an insulating medium.
It is known to employ sealed-off triggered vacuum switches (TVSs) to discharge a capacitor bank through the series combination of an inductor and a load resistor. It is also known to employ TVSs in the field of pulse power technology, such as a source controller in heavy laser and high power microwave, and in an electro-magnetic launcher (EML). Triggered spark gaps are known to be used in pulse power switching applications, such as in a Marx Bank.
There is room for improvement in arc flash arresters.
There is also room for improvement in switchgear systems including an arc flash arrester.
These needs and others are met by embodiments of the disclosed concept, which eliminate an internal arc flash from switchgear by diverting an uncontrolled arc flash into an envelope having a number of gaps disposed between conductors within the envelope.
In accordance with one aspect of the disclosed concept, a triggered arc flash arrester comprises: an envelope structured to operate at: (a) a pressure less than about 1.33 Pa; or (b) a pressure greater than 0.10857 MPa; a plurality of conductors partially disposed within the envelope; a number of gaps disposed between the plurality of conductors within the envelope; and a shorting structure selected from the group consisting of a triggered gap and a fuse, wherein the shorting structure is operatively associated with the number of gaps, and wherein the shorting structure is structured to electrically short the plurality of conductors either together or to ground, in order to create an arc within the envelope which is electrically in parallel to an arc fault causing the arc fault internal to switchgear to be extinguished.
The shorting structure may be the triggered gap; and the triggered gap may be formed by one of the plurality of conductors and an electrode disposed within and insulated from the one of the plurality of conductors.
The electrode may be an elongated electrode having a first end and an opposite second end; the one of the plurality of conductors may have a first opening proximate the first end of the elongated electrode and proximate another one of the plurality of conductors, and a second opening, larger than the first opening, proximate an insulator disposed between the elongated electrode and the one of the plurality of conductors; and the insulator may have a third opening, larger than and proximate the second opening, in order to prevent metal deposition on a surface of the insulator within the envelope between the elongated electrode and the one of the plurality of conductors.
The envelope may comprise a ring electrode; the shorting structure may be the triggered gap; and the triggered gap may be formed by a gap between the ring electrode and a cylindrical portion of one of the plurality of conductors.
The envelope may comprise a shield and a trigger rod electrode having a first end electrically connected to the shield and an opposite second end; the shorting structure may be the triggered gap; and the triggered gap may be formed by a gap between the opposite second end of the trigger rod electrode and a portion of one of the plurality of conductors.
The envelope may comprise a shield; the shorting structure may be the fuse; and the fuse may be electrically connected between the shield and one of the plurality of conductors.
The shorting structure may be the fuse; the envelope may comprise a ring electrode having a first portion disposed external to the envelope and a second portion disposed internal to the envelope; and the fuse may be electrically connected between the ring electrode and one of the plurality of conductors.
The envelope may further comprise an insulative cylinder disposed therein between the shield and the one of the plurality of conductors; the one of the plurality of conductors may have a cylindrical shape with a planar surface; the insulative cylinder may have an annular end parallel to the planar surface; and the annular end may support the fuse.
The annular end may have an outer edge proximate the shield and an inner edge proximate the one of the plurality of conductors; and the fuse may be disposed in a linear segment directly between the outer edge and the inner edge.
The annular end may have an outer edge proximate the shield and an inner edge proximate the one of the plurality of conductors; and the fuse may be disposed in a generally circular segment beginning at the outer edge, disposed over and around the annular end, and ending at the inner edge.
The shorting structure may be the triggered gap; and the triggered gap may be structured to be actuated by a number of voltage pulses having a voltage magnitude structured to breakdown the triggered gap.
The envelope may comprise a shield partially disposed within the envelope; the shield may not be electrically connected to any potential; and the triggered gap may be partially disposed within the shield.
The envelope may comprise a shield partially disposed within the envelope; the shorting structure may be the triggered gap; the triggered gap may be partially disposed within the shield; and the triggered gap may include a plasma exhaust disposed within the shield proximate the number of gaps and a trigger electrical connection disposed external to the envelope.
The envelope may comprise a ceramic tube having a ceramic surface therein and a shield partially disposed within the envelope; the shorting structure may be the triggered gap; the triggered gap may be partially disposed within the shield; and one of the plurality of conductors may have a shape structured to prevent metal deposition on the ceramic surface within the envelope.
As another aspect of the disclosed concept, a system comprises: switchgear including a power circuit; a triggered arc flash arrester comprising: an envelope structured to operate at: (a) a pressure less than about 1.33 Pa; or (b) a pressure greater than 0.10857 MPa, a plurality of conductors partially disposed within the envelope, a number of gaps disposed between the plurality of conductors within the envelope, and a shorting structure selected from the group consisting of a triggered gap and a fuse, wherein the shorting structure is operatively associated with the number of gaps, and wherein the shorting structure is structured to electrically short the plurality of conductors either together or to ground, in order to create an arc within the envelope which is electrically in parallel to an arc fault causing the arc fault internal to the switchgear to be extinguished; a current sensor sensing current flowing through the power circuit including a plurality of power conductors corresponding to the plurality of conductors; a light sensor sensing light operatively associated with the arcing fault for the power circuit; and a trigger circuit structured to trigger the shorting structure when the sensed current is greater than a first predetermined threshold and when the sensed light is greater than a second predetermined threshold.
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” or “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 “vacuum envelope” means an envelope employing a partial vacuum therein.
As employed herein, the term “partial vacuum” means a space (e.g., within a vacuum envelope) partially exhausted (e.g., to the highest degree practicable; to a relatively high degree; to a degree suitable for use in an arc flash arrester application; about 10−7 Torr) by a suitable mechanism (e.g., without limitation, an air pump; a vacuum furnace).
As employed herein, the term “atmospheric pressure” means force per unit area exerted against a surface by gas pressure. For example and without limitation, average sea-level pressure is 101.325 kPa (1013.25 mbar, or hPa) or 29.921 inches of mercury (in Hg) or 760 millimeters (mmHg, or Torr) or about 14.696 psi. Atmospheric pressure varies with different weather conditions and different altitudes above or below sea-level on the Earth. For example, the highest known barometric pressure ever recorded on Earth was 1,085.7 hectopascals (hPa) (or 0.10857 MPa) (or 32.06 in Hg) measured in Tonsontsengel, Mongolia on Dec. 19, 2001.
As employed herein, the term “low voltage” means a voltage up to about 1 kVRMS.
As employed herein, the term “medium voltage” means a voltage in the range from greater than a low voltage to about 38 kVRMS.
As employed herein, the term “high voltage” means a voltage greater than a medium voltage.
As employed herein, the term “arc flash arrester” means a shorting switch or other switching device structured to arrest or quench an arc flash or arcing fault by causing ionization and a subsequent breakdown of a main gap between open contacts (e.g., fixed and movable contacts; two or more fixed contacts).
As employed herein, the term “air” means the atmosphere of the planet Earth. Dry air contains, for example and without limitation, about (by volume) 78.09% nitrogen, about 20.95% oxygen, about 0.93% argon, about 0.039% carbon dioxide, and small amounts of other gases.
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.
Directional phrases used herein, such as, for example, top, bottom, front, back, left, right, upper, lower and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
The disclosed concept is described in association with one-phase and three-phase triggered arc flash arresters for low voltage or medium voltage operation, although the disclosed concept is applicable to a wide range of power circuit voltages and power circuits having any number of phases.
The disclosed concept employs either a triggered gap, such as a triggered spark gap, or a triggered fuse to cause electrical shorting of a plurality of conductors, either together or to ground, in order to create an arc within the envelope which is electrically in parallel to an arc fault causing the arc fault internal to switchgear to be extinguished. These provide, for example and without limitation, soft grounding, which can be an arc to ground or some arc impedance in the circuit as opposed to a solid metal-to-metal electrical connection.
Non-limiting examples of a triggered spark gap include: (1) trigger electrode rods (
Non-limiting examples of a triggered fuse include: (1) fuse ribbons (
Referring to
The example triggered arc flash arrester 2 employs the single envelope 4 for three phases (e.g., phases A, B and C) on the three conductors 8,10,12 and the ground 26 on the conductor 6, although any of the conductors 6,8,10,12 can be grounded. The envelope 4 can support a suitable partial vacuum, a pressure less than about 1.33 Pa, or a pressure greater than 0.10857 MPa (e.g., without limitation, 5 atmospheres). The conductors 6,8,10,12 can be fixed or stationary, or one of the conductors 8 or 12 can be movable (e.g., as in a vacuum switch or vacuum interrupter). For example, all of the conductors 6,8,10,12 being fixed provides for no moving parts, high speed operation and reliability. In the example embodiment, the triggered gap 24 is partially disposed within a shield 28, with a trigger electrode 30 exiting the envelope 4. The purpose of the shield 28 is to prevent metal deposition on the inside wall of the envelope 4 (e.g., without limitation, a ceramic bottle). If, for example, metal was deposited on the inside wall, then the envelope 4 might short out.
The example triggered arc flash arrester 2 can be employed, for example and without limitation, for medium voltage application. A short to ground 26 is created when the triggered gap 24 or triggered spark gap is triggered electronically. The spark causes metal ionization which, in turn, causes the number of gaps, such as 14,16,18,20,22, to breakdown thereby grounding the three phases on conductors 8,10,12. For example, the spark ionizes metal since it is, for example, in a partial vacuum. At pressures greater than one atmosphere, if sufficient energy is deposited in the spark gap or fuse, then the main switch contacts will breakdown. The metal vapor ions between the main gaps 14,16,18,20,22 cause them to breakdown.
The example conductors 6,8,10,12 and the shield 28 in the cross sectional view of
As will be discussed, the triggered gap 24 is structured to be actuated by a number of voltage pulses of suitable duration and having a voltage magnitude structured to breakdown the triggered gap 24. In this example, there are four conductors 6,8,10,12, and the three example phases (e.g., phases A, B and C) can be connected along with the ground 26 to any combination of these conductors.
The example envelope 4 includes the example shield 28 partially disposed within the envelope 4. In this example, the shield 28 is not electrically connected to any potential (e.g., ground; one of the three example phase voltages). The example triggered gap 24 is partially disposed within the shield 28, with the trigger electrode 30 exiting the envelope 4 and the shield 28. The example shield 28 is partially disposed within the envelope 4. The example triggered gap 24 includes an example plasma exhaust 25 disposed within the shield 28 proximate the number of gaps 14,16,18,20,22 and a trigger electrical connection formed by the trigger electrode 30 and the ground 26 disposed external to the envelope 4.
In this example, the number of gaps 14,16,18,20,22 are disposed between the conductors 6,8,10,12, and other gaps 32,34 are disposed between the shield 28 and the conductors 6,10. Although not required, as will be discussed below, these gaps 14,16,18,20,22,32,34 meet BIL spacing requirements.
The example triggered arc flash arrester 2 can be encapsulated in a suitable insulator, such as the example polyurethane molding 36 (partially shown for convenience of illustration), for increased BIL.
The example envelope 4 also includes a ceramic tube 38 having a ceramic surface 40 therein. The ceramic tube 38 insulates the shield 28 from the trigger electrode 30. The shield 28 preferably has a shape proximate the triggered gap 24 and the plasma exhaust 25 structured to prevent metal deposition on the ceramic surface 40 within the envelope 4.
The conductors 6,8,10,12 can be any suitable conductor (e.g., without limitation, copper-chrome; tungsten; copper; steel; an electrode of differing material on a copper conductor). The conductors 6,10 may optionally include a shield 42 thereon. The envelope 4 is formed by a number of cylindrical insulators (e.g., ceramic) 44,46, which are brazed to the respective conductors 10,6 at each end. The conductors 8,12 are insulated from the conductors 10,6 by cylindrical insulators (e.g., ceramic) 48,50, which are brazed to the conductors 10,6, respectively, at the top and bottom (with respect to
The example triggered arc flash arrester 102 employs the single envelope 104 for three phases (e.g., phases A, B and C) on the three conductors 108,110,106 and ground 126 on the conductor 112, although any of the conductors 106,108,110,112 can be grounded. The envelope 104 can support a suitable partial vacuum, a pressure less than about 1.33 Pa, or a pressure greater than 0.10857 MPa (e.g., without limitation, 5 atmospheres). The conductors 106,108,110,112 can be fixed or stationary, or one of the conductors 108 or 112 can be movable (e.g., as in a vacuum switch or vacuum interrupter). For example, all of the conductors 106,108,110,112 being fixed provides for no moving parts, high speed operation and reliability. In the example embodiment, the triggered gap 124 is partially disposed within conductor 112, with a trigger electrode 130 exiting the envelope 104. The purpose of the shield 128 is to prevent metal deposition on the inside wall of the envelope 104 (e.g., without limitation, a ceramic bottle). If, for example, metal was deposited on the inside wall, then the envelope 104 might short out.
In this example, the conductors 106,108,110,112 include example tungsten contact surfaces 106′,108′,110′,112′, respectively, brazed onto these conductors. These advantageously extend the contact life and reduce metal vapor deposits. The shield 142 of the conductors 106,110 has a step shape that creates a “shadow” over the ceramic tube 150, in order to prevent undesired metal deposition over the ceramic surface thereof.
The example conductors 106,108,110,112 and the shield 128 in the cross sectional view of
Although not required, the various gaps, such as 214,216,218 meet BIL spacing requirements. The example triggered arc flash arrester 202 can be encapsulated in a suitable insulator, such as the example polyurethane molding 236 (partially shown for convenience of illustration), for increased BIL.
The example triggered arc flash arrester 202 employs the single envelope 204 for three phases (e.g., phases A, B and C) on the three conductors 206,208,210. The envelope 204 can support a suitable partial vacuum, a pressure less than about 1.33 Pa, or a pressure greater than 0.10857 MPa (e.g., without limitation, 5 atmospheres). The conductors 206,208,210 in this example are fixed or stationary. This provides for no moving parts, high speed operation and reliability. In the example embodiment, the triggered gap 224 is partially disposed within shield conductor 228, with a trigger electrode 230 exiting the envelope 204. The purpose of the shield 228 is to prevent metal deposition on the inside wall of the envelope 204 (e.g., without limitation, a ceramic bottle). If, for example, metal was deposited on the inside wall, then the envelope 204 might short out.
The shields 28,128,228 of
Referring to
The envelope 304 can support a suitable partial vacuum, a pressure less than about 1.33 Pa, or a pressure greater than 0.10857 MPa (e.g., without limitation, 5 atmospheres). The conductors 306,308 can be fixed or stationary, or one of the conductors 306 or 308 can be movable (e.g., as in a vacuum switch or vacuum interrupter). For example, all of the conductors 306,308 being fixed provides for no moving parts, high speed operation and reliability. In the example embodiment, the triggered gap 324 is partially disposed within the conductor 308, with a trigger electrode 330 exiting the envelope 304. The purpose of the shields 328,328′,328″ is to prevent metal deposition on the inside wall of the envelope 304 (e.g., without limitation, a ceramic bottle). If, for example, metal was deposited on the inside wall, then the envelope 304 might short out.
The example triggered arc flash arrester 302 can be employed, for example and without limitation, for medium voltage application. A short to ground 326 is created when the triggered gap 324 or triggered spark gap is triggered electronically. The spark causes ionization which, in turn, causes the number of gaps, such as 314, to breakdown thereby grounding the single phase on conductor 306 to the ground 326 on the other conductor 308. The metal vapor ions between the main gap 314 causes it to breakdown.
The example conductors 306,308 and the shields 328,328′,328″ in the cross sectional view of
The triggered gap 324 is structured to be actuated by a number of voltage pulses 325 applied between the trigger electrode 330 and the ground 326 and have a voltage magnitude structured to breakdown the triggered gap 324.
Although not required, as will be discussed below, the main gap 314, for example, meets BIL spacing requirements. The example triggered arc flash arrester 302 can be encapsulated in a suitable insulator, such as an example polyurethane molding (not shown), for increased BIL.
The conductors 306,308 can be any suitable conductor (e.g., without limitation, copper-chrome; HC (high conductivity) copper; tungsten; copper; copper-tungsten; steel; an electrode of differing material on a copper conductor).
The envelope 304 is formed by a number of cylindrical insulators (e.g., without limitation, ceramic) 344,346, which are brazed to the conductors 306,310 (or end caps of the envelope 304) at each end.
The example envelope 304 also includes a ceramic tube 338 having a ceramic surface 340 therein. The ceramic tube 338 insulates the conductor 308 from the trigger electrode 330 (e.g., without limitation, tungsten). The conductor 308 preferably has a shape proximate the triggered gap 324 structured to prevent metal deposition on the ceramic surface 340 within the envelope 304, which otherwise could short the trigger electrode 330 to the conductor 308. The electrode 330 is elongated and has a first end 350 and an opposite second end 352. The conductor 308 has a first opening 354 proximate the first end 350 and proximate the other conductor 306, and a second opening 356, larger than the first opening 354, proximate the insulator 338 disposed between the elongated electrode 330 and the conductor 308. The insulator 338 has a third opening 358, larger than and proximate the second opening 356. This structure prevents metal deposition on the insulator surface 340 within the envelope 304 between the elongated electrode 330 and the conductor 308. As shown, the example openings 356,358 form an inverted T-shape.
For example and without limitation, for reliable triggering, the number of voltage pulses 325 have a negative polarity as applied to the trigger electrode 330 with respect to ground 326 with a magnitude of about −25 kVPEAK. Within the above stated pressure ranges, the pressure in the envelope 304 is believed to be no significant factor in trigger reliability. Preferably, however, a plurality of the voltage pulses 325 can be employed for increased reliability.
As shown in
Referring to
For example and without limitation, for reliable triggering, a number of voltage pulses applied between a terminal 438 of the ring electrode 404 and ground (e.g., conductor stem 412 as it exits the envelope 410) has a negative polarity as applied to the terminal 438 with respect to ground with a magnitude of about −17 kVPEAK. Alternatively, a positive polarity can be applied to the terminal 438 with respect to ground with a magnitude of about +26 kVPEAK. Preferably, however, a plurality of voltage pulses can be employed for increased reliability.
The example triggered arc flash arrester 502 can function, for example and without limitation, for a 38 kV system. Except for the trigger rod electrode 504 and external terminal 526, the envelope 508 can be the same as that for a conventional vacuum interrupter. As a further non-limiting example, the envelope 508 can be formed by a 5 inch diameter ceramic tube, and the conductors 518,522 can provide axial magnetic field (AMF) CuW contacts having a gap therebetween of about 13 mm. The conductors 518,522 can be fixed or stationary, or one of the conductors 518,522 can be movable (e.g., as in a vacuum switch or vacuum interrupter). A number of trigger voltage pulses can be applied between the terminal 526 and ground (e.g., conductor stem 528 as it exits the envelope 508).
In
The example triggered arc flash arresters 602,602′ can function, for example and without limitation, for a low voltage or medium voltage system. Except for the ring electrode 604 and fuse 606, the envelopes 610,610′ can be the same as that for a conventional vacuum interrupter with or without a shield. The lower (with respect to
In
In
As shown in
As shown in
As shown in
An example ceramic cylinder 930 isolates the shield 906 from the trigger rod electrode 904. Preferably, the outside of the envelope 908 is potted to prevent breakdown along, for example, the ceramic of the envelope 908 between the shield 906 and metal ring 932. An opening 934 (e.g., without limitation, about a 15 mm diameter hole) in the shield 906 allows the trigger rod electrode 904 to be isolated from the shield 906 in, for example and without limitation, a partial vacuum. This configuration results in a relatively more uniform electric field between the contacts for improved BIL.
The example triggered arc flash arrester 902 can function, for example and without limitation, for a 38 kV system. Except for the trigger rod electrode 904, example ceramic cylinder 930, metal ring 932, opening 934, and external terminal 926, the envelope 908 can be the same as that for a conventional vacuum interrupter. As a further non-limiting example, the envelope 908 can be formed by a 5 inch diameter ceramic tube, and the conductors 918,922 can provide axial magnetic field (AMF) CuW contacts having a gap therebetween of about 13 mm. The conductors 918,922 can be fixed or stationary, or one of the conductors 918,922 can be movable (e.g., as in a vacuum switch or vacuum interrupter). A number of trigger voltage pulses can be applied between the terminal 926 and ground (e.g., conductor stem 928 as it exits the envelope 908).
An example ceramic cylinder 1030 isolates the shield 1008 from the fuse 1006. Preferably, the outside of the envelope 1010 is potted to prevent breakdown along, for example, the ceramic of the envelope 1010 between the shield 1008 and the metal ring 1004. An opening 1034 (e.g., without limitation, about a 15 mm diameter hole) in the shield 1008 allows the fuse 1006 to be isolated from the shield 1008 in, for example and without limitation, a partial vacuum. This configuration results in a relatively more uniform electric field between the contacts for improved BIL.
A three-phase system, for example, can employ one of the three-phase devices of
Although example flat, planar contact surfaces are shown, any suitable vacuum interrupter contact surface can be employed (e.g., without limitation, spiral). For example and without limitation, contact and shield materials and contact and shield geometry depend on desired current and voltage ratings.
Although medium voltage trigger applications are disclosed, low voltage trigger applications can be employed with suitable changes to geometry spacing since BIL and rated voltages are much lower. As a result, the energy employed to trigger the triggered gap would be reduced.
Suitable trigger energy is employed to breakdown a partial vacuum triggered gap at an arcing voltage. When a switchgear arcing fault occurs, the voltage across the partial vacuum contacts, corresponding to the phase (e.g., one of three phases; a single phase) with the arcing fault, will have a significantly lower voltage across the contact gap as compared to the system voltage. The plasma energy produced from the triggered gap is sufficient to breakdown the main contact gap with this reduced voltage.
As non-limiting examples for
Preferably, the main contact gap is optimized. However, with a relatively larger gap, the greater the trigger energy needed to breakdown the main gap. An optimal gap is employed based on contact materials, contact diameter, contact gap, and surface condition. For example and without limitation, main gaps could range from about 2 mm to about 25 mm.
The main contact gap spacing is preferably reduced as much as possible. For vacuum interrupters (VIs), the limiting factor is generally not the system voltage but rather the BIL voltage requirement. However, the disclosed triggered arc flash arrester application is not an isolating switch but rather functions as a crowbar device. Hence, it is feasible to reduce the main contact gap to a distance that will breakdown at a BIL value lower than is typically required of VIs while maintaining BIL requirements on the external parts of the assembly. If, for example, a lightning strike occurred on a switchgear system, the impulse current would be diverted through the triggered arc flash arrester. This would serve two desirable purposes. One, the relatively smaller main gap would require relatively less shorting structure (e.g., triggered gap) energy to breakdown the main gap. Second, the triggered arc flash arrester could serve a dual purpose as a lightning protection system.
One problem that might be encountered during switching is metal deposition on the insulator (e.g., without limitation, ceramic) that surrounds the trigger electrode, which cannot become shorted out, unless the triggered arc flash arrester is intended for operation in a single arc flash event. Preferably, the insulator can either be recessed from a direct line of sight at the triggered gap, thereby shielding the insulator, or can be a recessed insulator hidden behind a step formed by the conductive contact in order to shield the insulator. Non-limiting examples are shown in
The triggered arc flash arresters disclosed herein can employ solely fixed contacts, or fixed and movable contacts. If movable vacuum contacts are employed, these may advantageously be employed to close the contacts to create a bolted fault on the system in order to reduce the stress on the vacuum switch. See, for example, the closed contact position of conductor 306 (shown in phantom line drawing in
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.
