Patent Grant
6952332
1. Field of the Invention
This invention relates to a vacuum arc interrupter and, more specifically, to a vacuum arc interrupter that utilizes a bullet assembly that is actuated by a gas generating source.
2. Background Information
There is the potential for an arcing fault to occur across the power bus of a motor control center (MCC), another low voltage (LV) enclosure (e.g., an LV circuit breaker panel), other industrial enclosures containing LV power distribution components, as well as medium voltage (MV) enclosures. 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.
It is known to employ a spring device and piston to rapidly couple a live conductor to a grounded conductor in a vacuum arc interrupter in order to short the circuit upstream of the LV components. A vacuum arc interrupter utilizes two contacts in a vacuum chamber. One contact is fixed and the other contact is movable. The movable contact includes a stem, which is coupled to a bellows, that extends outside of the vacuum chamber. The spring is coupled to the stem and to a release device. The release device is coupled to an arc sensor in the LV or MV enclosure. The stem, and therefore the movable contact, moves from a first position at one end of the chamber to a second position at the opposite end of the chamber. One contact is coupled to the LV or MV circuit and the other contact is grounded. In operation the first position of the piston corresponds to the open position of the contacts. When an arc occurs in the LV or MV equipment, the arc sensor actuates the spring release device, thereby allowing the contacts to move into the second position and short the circuit.
Another device, that is, a device which is not a vacuum arc interrupter, for shorting a circuit included a tapered slug which is propelled by high pressure gas into a tapered set of openings extending through two bus bars and a layer of insulation. The slug is maintained in a pressure chamber coupled to a gas-generating device. When gas is rapidly introduced to the pressure chamber, the slug is propelled into the tapered opening, contacting both bus bars. Typically, one bus is coupled to a live circuit and the other bus is grounded. Thus, when the slug contacts both buses, the circuit is shorted.
These interrupters suffer from several disadvantages. For example, the prior art vacuum arc interrupters require multiple components to be maintained in the vacuum chamber. Certain components, such as the bellows, are difficult and expensive to construct. Construction of the vacuum arc interrupter could be simplified if more components could be maintained outside of the vacuum chamber. Prior art vacuum arc interrupters utilizing springs, because of their nature, do not have a means for stopping the upward motion of the movable contact. That is, the spring mechanism is structured to absorb the reactive forces caused by the contacts colliding. Certain prior art vacuum arc eliminators also include a combination of springs and shock absorbers. The use of a spring or a combination of a spring and a shock absorber reduces, but does not eliminate, the bounce which occurs when the moving component contacts the stationary component. Thus, the prior art vacuum arc interrupters do not have a mechanism for stopping the advance of the moving component.
Furthermore, with regard to the prior art utilizing a slug, the slug relied on the application of gas pressure on the piston to ensure that the piston remained in the second position. Or, if the slug moved in a downward direction and the slug was heavy, gravity provided a sufficient force to hold the slug in place. That is, this system did not include a mechanical lock to maintain the slug in the second position. Additionally, the prior art slugs have a generally flat pressure surface. Because the gas is typically introduced through a small opening, the pressure distribution on the slug pressure surface is uneven. The uneven pressure distribution prevents the slug from moving as fast as a slug where the pressure distribution is even. Another disadvantage of this device is that, where the slug is received in a conductor having a small cross-sectional area, the electromagnetic field created by the contact may by very strong.
There is, therefor, a need for a vacuum arc interrupter that closes a circuit as rapidly as a device utilizing a slug.
There is a further need for vacuum arc interrupter that utilizes a gas generation device.
There is a further need for a vacuum arc interrupter that utilizes a first conductor maintained within a vacuum chamber and a second conductor disposed outside of the vacuum chamber.
There is a further need for a vacuum arc interrupter that utilizes a bullet assembly to electrically link two conductors where a first conductor is maintained within a vacuum chamber and the second conductor is disposed outside of the vacuum chamber.
These needs, and others, are satisfied by the disclosed invention which provides a vacuum arc interrupter having a vacuum chamber assembly and an adjacent pressure chamber assembly. A first conductor is within a vacuum chamber in the vacuum chamber assembly, and a second conductor, which is part of the pressure chamber assembly, is disposed outside of the vacuum chamber. The two conductors are electrically coupled by a bullet assembly. The bullet assembly includes a conductive lance. The bullet assembly is slidably disposed within a pressure chamber in the pressure chamber assembly. The bullet assembly is originally in a first position where the entire bullet assembly is disposed is within the pressure chamber. When the pressure in the pressure chamber is rapidly increased by a gas generation device, the bullet assembly moves to a second position where the lance contacts the second conductor and extends beyond the pressure chamber assembly to contact the first conductor. To access the first conductor, the lance punctures a seal that is integral to the vacuum chamber assembly.
The pressure chamber includes a first sized portion and a second sized portion. Both the first sized portion and the second sized portion have a generally constant cross-sectional area, with the first sized portion having a smaller cross-sectional area than the second sized portion. Between the first sized portion and the second sized portion is a transition portion. The transition portion has a cross-sectional area that tapers from the cross-sectional area of the first sized portion to the cross-sectional area of the second sized portion. The first sized portion is in fluid communication with an inlet port opening. The inlet port opening is coupled to, and in fluid communication with, the gas generating device. The second sized portion is in fluid communication with a bullet assembly opening.
The bullet assembly includes a piston assembly and the lance. The bullet assembly piston assembly has a first side and a second side. Hereinafter, the first side will be the side exposed to the gas generating source and therefore may also be referred to as the pressure surface. The piston assembly pressure surface is not flat. As such, gas from the gas generating source is dispersed across the surface of the pressure surface thereby reducing areas of localized pressure. The pressure surface may be either concave or convex. Preferably, the pressure surface is convex, and, where the piston is circular, conical. The conical surface, preferably, has a more obtuse angle than the angle of the taper of the pressure chamber transition portion. As such, there is a gap between the pressure surface and the sidewall of the transition portion. In use, when the gas generation source is activated, the gas entering the chamber first sized portion and the chamber transition portion contacts the conical surface and is dispersed in the gap. The dispersal of the gas creates an even pressure distribution on the pressure surface and causes the piston to move from a first position adjacent to the transition portion to a second position away from the transition portion.
The bullet assembly lance is made from a conductive material and includes an elongated body having a tapered tip and a flared base. The tapered tip is structured to engage a cup on a first conductor, where the cup has a cavity corresponding to the shape of the lance tip. Alternatively, the cup may have a cavity that partially corresponds to the shape of the lance tip, thereby having an interference fit. The flared base is structured to correspond to the shape of a tapered passage in a conductor. The lance is sized so that as the flared base engages the tapered opening in one conductor, the tip firmly engages the cup disposed on the other conductor. Thus, the lance acts to electrically couple the two conductors.
In operation, the vacuum arc interrupter has one conductor, typically the first conductor, coupled to, and in electrical communication with, a circuit. The second conductor is coupled to, and in electrical communication with, a ground. The circuit includes a low voltage or medium voltage device at a point downstream of the vacuum arc interrupter. The low voltage or medium voltage device includes an arc detector which is coupled to and structured to activate the gas generating device. When an arc is detected in the low voltage or medium voltage device, the gas generating device generates a gas which flows into the pressure chamber first sized portion and the transition portion gap. The gas generating device delivers gas at a pressure about 180 psi, through the inlet port into the chamber first size portion. This increase of pressure occurs in about 0.5 msec and causes the bullet assembly to move from the first position to the second position in less than 2.0 msec. Because the inlet port opening is on the piston first side, gas from the gas generating device will flow into the chamber first sized portion and transition portion and contact the angled piston first side. The angle of the piston first side assists the gas in dispersing through the chamber transition portion and thus creates an even pressure distribution on the piston first side. As the bullet assembly moves from the first position to the second position, the lance passes through a tapered passage in the second conductor causing the lance to puncture the seal on the vacuum chamber. The flared base is sized to correspond to the tapered opening. Thus, when the flared base contact the tapered passage, the motion of the bullet assembly is stopped. At this the same time the flared base contacts the tapered passage, the lance tip contacts the first conductor, thereby electrically coupling the two conductors.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As shown in
The non-conductive housing 18 is made from a non-conductive material, preferably a ceramic. The non-conductive housing 18 has a shape that corresponds to the shape of the first conductor 16. Thus, when the first conductor 16 has a disk shape, the non-conductive housing 18 is a hollow cylinder. One axial end of the non-conductive housing 18 is sealingly coupled to the first conductor 16.
The seal cup 20 includes a generally planar base member 32 and a sidewall 34 generally perpendicular thereto. The seal cup 20 is made from a rigid, non-brittle material such as a cupro-nickel alloy. The alloy material preferably has between about 50 to 95% copper, and more preferably about 70% copper, and between about 5 to 50% nickel, and more preferably about 30% nickel. The alloy may also have lesser amounts of other elements or impurities. Generally, the seal cup 20 material may be torn without a substantial amount of fragmentation. The seal cup sidewall 34 is sealingly coupled to the axial end of the non-conductive housing 18 opposite the first conductor 16. Thus, the combination of the first conductor 16, the non-conductive housing 18, and the seal cup 20 define a vacuum chamber 36. As will described hereinafter, the seal cup 20 contacts the second conductor 70. To prevent an arc from forming within the vacuum chamber 36, the first conductor 16, or the electrode 23 if present, and the seal cup 20 are separated by a distance sufficient to lower the magnitude of the electric field to below that which would lead to an electrical breakdown within the vacuum. This distance is, generally, about 0.4 inch to 2.0 inches and varies depending upon the voltage in the system. For example, for a voltage of about 125 kilovolts, the distance is preferably about 0.6 inch.
To reduce the magnetic field at the point where the seal cup 20 is attached to the non-conductive housing 18, a ring shaped metal may extend into the vacuum chamber 36 from the seal cup 20. The shield extends adjacent to the seal cup side wall 34 and has a height sufficient so that the shield is disposed between the point where the seal cup 20 is attached to the non-conductive housing 18 and the electrode 23. Additionally, there may be an upper seal cup, similar to the seal cup 20 described in detail above, disposed between the first conductor 16 and the ceramic housing 18. The upper seal cup includes an opening to allow the stem 25 to pass therethrough.
The pressure chamber assembly 14 includes a gas generation device 40, a pressure chamber body 42, a second conductor 70, and a bullet assembly 46. The gas generation device 40 may be any gas generation device such as those manufactured by TRW Airbag Systems GmbH & Co. KG, Wernher-Von-Braun-STR. 1, D-84544 Asehan am Inn, Germany.
The pressure chamber body 42 is preferably cylindrical and includes a barrel 50 and a mounting flange 51. The barrel 50 has a first end 52 and a second end 54. The barrel 50 has an inlet port opening 56 on the first end 52 and a bullet assembly opening 58 at the second end 54. The inlet port opening 56 is smaller than the bullet assembly opening 58. The inlet port opening 56 is in fluid communication with the bullet assembly opening 58. Thus, the barrel 50 defines a pressure chamber 60. The pressure chamber 60 includes a first sized portion 62, a transition portion 64, and a second sized portion 66. The first sized portion 62 has a smaller cross-sectional area than the second sized portion 66. The first sized portion 62 is in fluid communication with the inlet port opening 56. The second sized portion 66 is in fluid communication with the bullet assembly opening 58. The transition portion 64 is disposed between, and in fluid communication with, the first sized portion 62 and the second sized portion 66. The transition portion 64 has a cross-sectional area that tapers from the cross-sectional area of the first sized portion 62 to the cross-sectional area of the second sized portion 66. The pressure chamber 60 preferably has a generally circular cross-sectional area. The flange 51 extends radially from the barrel second end 54 and includes a plurality of fastener openings 53.
The second conductor 70 is made from a conductive material and, preferably, is shaped as a circular disk. The second conductor 70 may include a radial extension 72 having an attachment opening 74 therethrough. The attachment opening 74 is structured to allow a ground line to be coupled to the second conductor 70. The second conductor 70 has a first side 76 and a second side 78. The second conductor 70 also includes a tapered passage 80, preferably medially disposed on the disk. The tapered passage 80 has a first sized opening 82 on the second conductor first side 76 and a second sized opening 84 on the second conductor second side 78. The first sized opening 82 is larger than the second sized opening 84. Thus, the tapered passage 80 has a tapered sidewall 86 extending between the openings 82, 84. The tapered passage 80 is tapered at an angle θ corresponding to the angle of the flare of the lance base portion 120, described below. As described hereinafter, typically a power line is coupled to the first conductor 16 and a ground line is connected to the second conductor 70.
The bullet assembly 46 includes a piston assembly 90 and a lance 110. The piston assembly 90 includes a piston body 92, and may include a piston ring 94. The piston body 92 is a solid body which is generally planar having a first side 96, a second side 98, and a sidewall 100. The piston body 92 has the same general cross-sectional shape and size as the pressure chamber second portion 66 and is structured to be slidably disposed therein. The sidewall 100 includes a groove 101 wherein the piston ring 94 may be seated. The piston first side 96 is not flat having either a concave surface, see
The lance 110 includes an elongated body 112 having a first end 114 and a second end 116. The lance body 112 includes a tip 118 disposed at the first end 114 and a base 120 disposed at the second end 116. Between the tip 118 and the base 120 is a medial portion 122. The tip 118 tapers to an edge or a point. The end of the tip 118 acts as a blade portion 124 to assist in cutting the seal cup 20 as described below. The angle of the tip taper, α, is between about 90 and 150 degrees and preferably about 120 degrees as measured from a line parallel to the outer surface of the surface of the medial portion 122. The medial portion 122 preferably has a constant cross-sectional area. The medial portion 122 preferably has a circular or square cross-section. As shown in
The bullet assembly 46 is formed when the lance 110 is coupled to the piston assembly 90 by coupling the lance attachment device 125 to the piston attachment device 102. Thus, the lance 110 extends from the piston second side 98. The lance 110 has a length sufficient to span the gap between the second conductor 70 and the cup 26. The lance 110 is, however, sized so that the flared base 120 contacts the second contact tapered opening as the tip 118 contacts the cup 26.
The pressure chamber assembly 14 is formed by inserting the bullet assembly 46 into the chamber second size portion 66 with the lance 110 extending toward the bullet assembly opening 58. The bullet assembly 46 is disposed in a first position where the piston body 92 is in the pressure chamber second sized portion 66 and adjacent to the chamber transition portion 64, with the lance 110 extending into the second sized portion 66. The lance 110 does not, however, extend beyond the bullet assembly opening 58. Because the piston body first side 96 has a taper angle that is more obtuse that the taper angle of the pressure chamber transition portion 64, a gap exists between the piston body first side 96 and the pressure chamber transition portion 64. The piston ring 94 engages the sidewall of the chamber second sized portion 66. The second conductor 70 is coupled to the pressure chamber mounting flange 51 by fastener 53 with the second conductor first side 76 disposed toward the pressure chamber 60. Thus, the larger, first sized opening 82 of the tapered passage 80 is adjacent to the bullet assembly 46. The gas generation device is coupled to, and in fluid communication with, the inlet port opening 56.
In this configuration, the bullet assembly 46 is structured to move from the first position, described hereinbefore, to a second position, shown in
Accordingly, to assemble the vacuum arc interrupter 10, the vacuum assembly 12 is coupled to the pressure chamber assembly 14 with the seal cup 20 contacting, and in electric communication with, the second conductor 70. In this configuration, translation of the bullet assembly 46 from the first position to the second position will result in the lance blade portion 124 piercing the seal cup 20 and the lance 110 contacting the first conductor cup 26. As stated hereinbefore, the lance 110 is sized such that the tip 118 engages the cup 26 at the same time the flared base 120 engages the second contact tapered passage 80. Thus, when the bullet assembly 46 is in the second position, the first and second conductors 16, 70 are in electrical communication.
In operation, the bullet assembly 46 is moved from the first position to the second position by the gas-generating device 40. That is, the gas generating device 40 delivers gas at a pressure between about 180 and 375 psi, and preferably about 180 psi, through the inlet port opening 56 in to the chamber first size portion 62. This increase of pressure occurs in about 0.50 msec and causes the bullet assembly 46 to move from the first position to the second position in less than 2.0 msec. Because the inlet port opening 56 is on the piston first side 96, gas from the gas generating device will flow into the chamber first sized portion 62 and transition portion 64 and contact the angled piston first side 96. The angle of the piston first side 96 assists the gas in dispersing through the chamber transition portion 64 and thus creates a more even pressure distribution on the piston first side 96. As the bullet assembly 46 moves from the first position to the second position, the lance tip 118 and medial portion 122 pass through the tapered passage 80 causing the blade portion 124 to puncture the seal cup planar member 32. Because the seal cup 20 is made of a cupro-nickel material, the seal cup 20 is torn as opposed to fragmenting.
As stated hereinbefore, the lance tip 118 engages the cup 26. If the lance tip 118 is conical, the taper of the tip 118 and the taper of the cup 26 sidewall is, preferably, similar. Thus, the lance 110 and the cup 26 cooperatively engage each other. If, however, the lance tip 118 is pyramidal, the lance 110 and cup 26 will engage in a mechanical connection as the square lance 110 collides with the circular cup 26. This collision will form a mechanical connection that may be enhanced if an arc forms between the lance 110 and the cup 26 thereby partially melting either the lance 110 or the cup 26. Additionally, after the downstream arc is interrupted and electricity is flowing through the vacuum arc interrupter 10, heat generated in the flared base 120 and the second contact tapered passage 80 will partially melt the metal components and form a weld. As such, the bullet assembly 46 is mechanically locked by a weld to the second conductor 70.
As shown in
Aspects of this invention may also be used in conjunction with an alternate embodiment of the vacuum arc interrupter 210 having two contacts in a vacuum chamber assembly 200. That is, as shown in
While specific embodiments of the invention 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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
This application is related to commonly assigned, concurrently filed: U.S. patent application Ser. No. 10/172,208 filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment”, now U.S. Pat. No. 6,724,604; U.S. patent application Ser. No. 10/172,651, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment”, now U.S. Pat. No. 6,657,150; U.S. patent application Ser. No. 10/171,826, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Low Voltage Power Distribution Equipment”, now U.S. Pat. No. 6,633,009; U.S. patent application Ser. No. 10/172,238, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment”; U.S. patent application Ser. No. 10/172,622, filed Jun. 14, 2002, entitled “Bullet Assembly For A Vacuum Arc Interrupter”; U.S. patent application Ser. No. 10/172,080, filed June 14, 2002, entitled “Vacuum Arc Interrupter Having A Tapered Conducting Bullet Assembly”; U.S. patent application Ser. No 10/172,209, filed June 14, 2002, entitled “Vacuum Arc Interrupter Actuated By A Gas Generated Driving Force”; and U.S. patent application Ser. No. 10/172,628, filed June 14, 2002, entitled “Blade Tip For Puncturing Cupro-Nickel Seal Cup”.
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| Number | Date | Country | |
|---|---|---|---|
| 20030231438 A1 | Dec 2003 | US |
