SEALED HIGH TENSION CONTACTOR

Abstract: A hermetically sealed contactor (10) of the magnetic blowout type is provided utilizing a novel arc chute design (14). The fins (60) of the arc chute (14) include an angled leading edge (67) and a tapered body (38) for slowing and confining the arc in the chute (14) until extinction. The housing (16) is back pressurized with a highly thermally conductive gas to assist in removing heat from the arc, permitting the use of a smaller and simpler contactor (10) arrangement, while maintaining the performance realized in larger devices.

Description: SEALED HIGH TENSION CONTACTOR FIELD OF THE INVENTION The present invention relates to contactors adapted for connecting and interrupting current in electrical circuits, and more particularly to a hermetically sealed contactor pressurized with a highly thermally conductive gas, wherein the contactor has an improved arc chute design. BACKGROUND OF THE INVENTION Contactors of the magnetic arc blowout type have been used for the connection and interruption of relatively high electrical circuits currents. The contactors include an arc chute for quenching arcs that form upon interruption of heavy currents. Existing devices used for this purpose are typically operated unsealed as open-air contactors. This unconfmed operation, however, poses certain safety concerns in terms of arc containment, and often causes excessive noise. In addition, many of the existing devices are large and complex with respect to the arc chute assemblies. Consequently, a need exists for an improved contactor for use in such applications. SUMMARY OF THE INVENTION The present invention provides an improved contactor of the magnetic blowout type hermetically sealed in a container which is pressurized with a highly thermally conductive gas. The contactor includes a switching mechanism and a novel arc chute assembly. The switching mechanism includes a pair of separable contacts between which an arc is drawn during interruption of an external circuit current. An arc blowout unit is provided for generating a magnetic field during interruption of the circuit current to drive the arc into the arc chute. The novel arc chute assembly controls the expulsion of the arc plasma via the geometry of the chute labyrinth. The arc chute includes a pair of sidewalls, each sidewall including a plurality of chute fins projecting toward the other sidewall, the fins arranged to mutually interleave with the corresponding fins on the other sidewall. This interleaving produces a zigzag path through the chute between the arc runners for increasing the surface area within the chute labyrinth. Each fin includes an angled leading edge proximate the entrance to the arc chute. The edge is angled to help slow down the arc as it passes through the entrance. The fins gradually taper in width from an exit of the arc chute to the entrance of the arc chute. This tapering of the chute fin body also serves to gradually lengthen the arc within the arc chute. The hermetically sealed housing enables the contactor to be immersed in a pressurized chamber of thermally conductive gas. This serves to reduce the span of the arc chute and the number of fins required to recover the arc voltage and drive the circuit current to zero. In a presently preferred embodiment, the housing is back pressurized with a mixture of hydrogen and nitrogen. The above-described features work in combination to aid in recovering arc voltage in a significantly smaller and simpler arrangement while maintaining the performance realized in existing larger and more complicated devices. Moreover, the sealed containers provide added safety and reduced noise, which increases the desirability of the contactor in new and existing applications. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will be appreciated as the same become better understood by reference to the following Detailed Description when considered in connection with the accompanying drawings, wherein: FIG. 1 is a plan view of the contactor according to the present invention, with the lid of the housing removed and one of the yoke plates shown in phantom; FIG. 2 is a cross sectional view of the contactor of FIG. 1, taken along line 2-2; FIG. 3 is a cross sectional view taken along line 3-3 and illustrates the arc chute fins of the contactor of FIG. 1; FIG. 4 is a plan view of the contactor according to the present invention, with the lid of the housing and one of the yoke plates removed; and FIG. 5 is a perspective view of the switch mechanism and arc chute assembly of the contactor of FIG. 4. DETAILED DESCRIPTION Referring to FIG. 1, a presently preferred embodiment of the contactor 10 according to the present invention includes a switch mechanism 12 and an arc chute assembly 14 contained within a hermetically sealed housing 16. The housing 16 includes a base section 18 and a matching lid 15 for sealing the housing. An insulating carrier 70, consisting of a top portion 17 and a bottom portion 19, is contained within the housing for receiving the switch mechanism and the arc chute assembly. The housing is preferably aluminum or stainless steel. The switch mechanism 12 connects and interrupts current from an external circuit (not shown). The external circuit may be used in conjunction with a wide variety of applications, including, for example, those used in electric rail car, electric car, or any other power feed or distribution system application requiring relatively high current connection and interruption. The switch mechanism includes a stationary contact 20 and a movable contact 22. An actuator 23 connected to a shaft 26 of the moveable contact operates the moveable contact between closed and open circuit positions. In the open circuit position shown in FIG. 1 , a contact gap 24 exists between the stationary and movable contact, in which the arc is formed. An arc blowout unit 28 is provided in electrical connection with the stationary contact for generating a magnetic field during current interruption. The blowout unit includes a blowout coil 30 wrapped around a ferromagnetic core 32. The metallic core is preferably, made of iron, although other suitable magnetic materials well known in the art may also be used. FIG. 1 shows the use of a cylindrical core 32. Alternatively, as shown in FIG. 4, a rectangular core 33 may also be used. The stationary contact 20 and moveable contact 22 are electrically connected to the external circuit via a flexible conductor 40 and an extension 42 of the blow-out coil 30, respectively. Both connections are afforded passage through the housing 16 by hermetic seals 44, 46 located at an end 38 of the housing. Epoxy is preferably used to form the hermetic seals 44, 46. The contacts are connected to conductive arc runners 48, 50. The stationary contact 20 is connected to a first arc runner 48 and the movable contact 22 is connected to a second arc runner 50. An arc-current connector 51 is used to connect the moveable contact 22 to the lower arc runner 50. In normal current carrying operation, current flows through the closed contacts via the blowout coil and flexible conductor. Upon opening of the contacts, an arc strikes in the contact gap as the contacts part. The arc is almost immediately moved out to the arc runners under the influence of the magnetic field generated by the current still flowing through the blowout coil. The arc runners 48, 50 direct the arc formed between the contacts toward the arc chute 14. The arc runners extend through the contactor along an upper edge 52 and a lower edge 54 of the arc chute. The upper arc runner 48 extends along the upper edge 52 of the arc chute and the lower arc runner 50 extends along the lower edge 54 of the arc chute. Yoke plates 34, 36 help distribute the magnetic field generated in the blowout unit uniformly throughout the contactor. The yoke plates project through the contactor from opposite ends of the core on either side of the arc chute 14. Yoke plate 34 is shown in phantom in FIG. 1. The yoke plates preferably extend beyond the entrance 38 of the arc chute a certain distance so that the arc is properly driven toward the chute. If the yoke plates do not extend beyond the entrance, the arc may not be sufficiently driven into the chute. Conversely, if the yoke plates extend too far beyond the entrance, the arc may be forced through the chute before it is extinguished. Therefore, in the preferred embodiment the yoke plates are designed to extend beyond the entrance 38 approximately one-quarter to one-half the length of the arc chute. The arc chute 14 is positioned with respect to the switch assembly 12 so as to directly receive the arc formed during interruption of the external circuit current. The arc chute comprises a pair of spaced sidewalls 56 and 58 of suitable arc-resistant insulating material. In a presently preferred embodiment, the arc chute is formed from CORDIERITE, which is commercially available from Hoechst CeramTec in Mansfield, Massachusetts. Referring to FIG. 2, each sidewall of the arc chute includes a plurality of chute fins 60 projecting toward the other sidewall. The chute fins on each sidewall are arranged to mutually interleave with corresponding projecting fins on the other sidewall. The interleaving of the fins forms a zigzag path 62 through the chute between the arc runners when viewed from the exit 64 of the chute. Referring now to FIGS. 1 and 3, the chute fins 60 are shaped to provide a gradual stretching of the arc in all dimensions so that the arc is gradually forced to lengthen and cool on the insulating surfaces of the chute fins. The leading edge 67 of the fins is angled to help gradually guide the arc into the entrance of the arc chute, permitting the arc to enter the chute without causing stalling. The leading edge angle helps to efficiently counter the momentum of the arc as it is driven into the chute assembly. The angle Θ (FIG. 3) is the angle measured from the sidewall of arc chute assembly to the leading edge of the fins. The specific value of Θ required will depend on a number of factors, including but not limited to the load conditions and size of the contactor. Additionally, the chute fins 60 are tapered depending on the characteristics of the external circuit. If tapering is desired, the body of the fins gradually taper in width from the exit 66 of the arc chute to the entrance 38 of the arc chute. The tapering of the chute fin body provides for a gradual lengthening of the arc. Specifically, the taper angle provides a hydrodynamic resistance to the arc, slowing and confining the arc in the chute assembly until extinction. The taper exposes the arc to an increasingly larger surface area and mass of insulating material, which aids in removing energy from the arc. As an added feature, in the preferred embodiment a notch 68 is provided in the chute fins 60 near the exit 66 of the arc chute. The notch provides a means for break-up and deionization of the arc near current-zero. As the arc travels into the entrance of the arc chute, it is gradually forced to lengthen and cool on the insulating surfaces of the chute fins. The geometry of the fins and the chute labyrinth work in combination to slow and confine the arc in the chute labyrinth until extinction. The contactor is preferably hermetically sealed to help extinguish the arc, reduce noise and reduce the size and complexity of the contactor. To facilitate hermetic sealing of the contactor components, the elements comprising the switching mechanism may be assembled into an insulating carrier 70 prior to insertion into the housing along with the arc chute. Once this is complete, the lid may be installed onto the housing and seam welded to complete the housing seal. The advantage of the hermetically sealed housing is that it permits immersing the switch mechanism and arc chute assembly in a thermally conductive gas under pressure. Filling the housing with a thermally conductive gas has a significant effect on reducing the span of the arc chute and the number of fins required to recover the arc voltage required to drive the circuit current to zero. After sealing is complete, the entire housing is evacuated and back pressurized via a tubulation 72 with a thermally conductive gas. The tubulation is then swaged closed to complete the sealing operation. The pressurized atmosphere inside the contactor removes heat from the arc as it proceeds through the chute. In a preferred embodiment, the contactor is pressurized with a mixture of hydrogen and nitrogen, the mixture and pressure of which may be varied to meet the requirements of the external circuit. It has been experimentally determined that the partial pressure of hydrogen in the mixture is preferably about 25% to about 100% of the total pressure of the mixture. In general, in inductive load conditions, higher hydrogen concentration and/or pressure reduces the break arc duration, but increases the peak arc voltage developed across the contacts. The preferred pressure to which the contactor is back pressurized may depend on a number of different factors. For example, due to the presence of transient voltages in inductive load conditions, lower pressures are generally preferred. Alternatively, in resistive load conditions, higher pressures are generally preferred due to the resulting increased quenching ability of the atmosphere within the contactor. Preferably, the contactor is back pressurized to about one-half to five atmospheres. While this is merely a preferred range, it should be noted that there may be inherent limitations at both ends of this range. At the lower end of the preferred range (e.g. below one atmosphere) there is the risk of Paschen breakdown that occurs at partial pressures. Additionally, at lower levels of pressure the "snubber" effect of the thermally conductive atmosphere inside the contactor is less effective. By way of contrast, the upper end of the preferred pressure range may be constrained by the structural integrity of the contactor housing. The presently preferred values for Θ and β and the constituent mix and fill for the gasses depend in part on the operating range of the circuit current and whether the load is substantially inductive or resistive. The values have been experimentally derived based on an industry guideline of allowable peak arc voltage at 2.5 times the source voltage. The leading edge angle and taper of the chutes help to balance the magnetic forces on the arc, which are generally in proportion to the peak interruption current. In general, the chute fins are preferably designed to have a leading edge angle Θ in the range of about 30 degrees to about 90 degrees. Lower values of leading edge angle Θ may not provide enough impedance to counter the momentum of the arc, permitting the arc to blow through the chute and restrike on the outside of the chute. Conversely, greater values of leading edge angle Θ may result in too much physical resistance to the arc, causing stalling of the arc at the entrance of the arc chute. Likewise, the chute fins are in general preferably designed to have a taper angle β in the range of about 0 degrees to about 5 degrees. Lower values of taper angle β in this range are better suited for low current, low voltage applications. Greater values of taper angle β outside this range may not provide necessary resistance at the entrance of the arc chute to effectively remove heat from the arc. For inductive loads (i.e., having an inductance to resistance ratio (L/R) of approximately 15 ms) in which the range of current is less than or equal to about 1000 A, it has been shown that the preferred value for Θ is about 40 degrees, the preferred value for β is 0 degrees (i.e., no taper) with an approximately even mix of hydrogen (H 2 ) and nitrogen (N back pressurized to 1-2 atmospheres. For inductive loads having a current range between about 1000A and 1600A, it has been shown that the preferred value for Θ is about 60 degrees, the preferred value for β is about 1.8 degrees with about 75% H 2 and about 25% N 2 , back pressurized to 2-3 atmospheres. For resistive loads in which the range of current is less than or equal to about 2000 A, it has been shown that the preferred value for Θ is about 40 degrees, the preferred value for β is about 0 degrees (i.e., no taper) with an approximately even mix of H 2 and N 2 , back pressurized to 1 -2 atmospheres. For resistive loads in which the range of current is between about 2000 A and 2500A, it has been shown that the preferred value for Θ is about 60 degrees, the preferred value for β is about 1.8 degrees with about 75% H 2 and about 25% N 2 , back pressurized to about 2-3 atmospheres. The novel design of the contactor, in particular the unique chute design sealed in a thermally conductive gas chamber, permits an overall reduction in size of approximately 50% compared with existing contactors. By way of example, the arc chute contained in the contactor illustrated in FIG. 4 is about 6 inches wide. It should be realized, however, that the size of the contactor depends on a number of different factors, including the intended application, source voltage and circuit current. FIG. 4 also illustrates the preferred positioning of the arc chute within the housing, so that a gap 71 exists between the exit of the arc chute and the housing. Although the size of the gap 71 also depends on a number of different factors, it has been shown that the gap is preferably at least about V2 inch. The contactor is also an improvement over the existing devices due to the added safety and reduced noise afforded by the sealed housing. It will be understood that the foregoing is merely illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the spirit and scope of the invention as defined by the following claims. For example, the contacts, runners, and the arc blowout circuit may assume any suitable form well known in the art. The mixture of the gasses can also be varied to optimize operation of the contactor depending on the characteristics of the particular external circuit with which it is used. Therefore, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims: CLAIMS 1. A contactor for connecting and interrupting an electric circuit, the contactor comprising: a switching apparatus including a pair of relatively movable contacts between which an arc may be formed upon interrupting the circuit; an arc chute assembly into which the arc is driven to extinguish the arc; an arc blowout unit for driving the arc from the switch assembly into the arc chute; and a hermetically sealed housing containing the switching apparatus, the arc chute assembly and the arc blowout unit; wherein the arc chute assembly includes a plurality of chute fins projecting inwardly in an interleaving manner from a pair of spaced sidewalls, and wherein the housing is pressurized with a thermally conductive gas. 2. The contactor according to claim 1 wherein the thermally conductive gas is a mixture of hydrogen and nitrogen. 3. The contactor according to claim 2 wherein partial pressure of hydrogen in the mixture is about 25% to about 100% of total pressure of the mixture. 4. The contactor according to claim 1 wherein each of the plurality of chute fins comprises an angled leading edge near an entrance of the arc chute. 5. The contactor according to claim 4 wherein the angled leading edge of the chute fins is angled at about 30 degrees to about 90 degrees from the sidewall. 6. The contactor according to claim 5 wherein the angled leading edge of the chute fins is angled at about 60 degrees. 7. The contactor according to claim 4 wherein each of the plurality of chute fins further comprises a tapered body, the body tapering from an exit of the arc chute to the entrance of the arc chute. 8. The contactor according to claim 7 wherein the tapered body of the chute fins tapers at an angle of about 0 degrees to about 5 degrees. 9. The contactor according to claim 8 wherein the tapered body of the chute fins tapers at an angle of about 1.8 degrees. 10. The contactor according to claim 7 wherein each of the plurality of chute fins further comprises a notch near an exit of the arc chute. 11. The contactor according to claim 1 wherein the housing is pressurized at about 1/2 an atmosphere to about 5 atmospheres. 12. The contactor according to claim 1 wherein the housing is pressurized at about 1 atmosphere to about 3 atmospheres. 13. A contactor adapted for connecting and interrupting current in electrical circuits, the contactor comprising: arc drawing means for drawing an arc during interruption of the current from the electrical circuit; an arc chute including a pair of substantially oppositely facing sidewalls, wherein each sidewall includes a plurality of chute fins projecting toward the opposite sidewall, and wherein the fins on one sidewall are arranged to mutually interleave with the fins on the opposite sidewall; and arc driving means for driving the arc into the arc chute. 14. The contactor of claim 13 further comprising sealing means for hermetically sealing the arc drawing means, the arc chute, and the arc driving means. 15. The contactor of claim 14 wherein the sealing means comprises a thermally conductive gas. 16. A contactor for connecting and interrupting an electric circuit, the contactor comprising: a switch; an arc chute assembly comprising a plurality of interleaved arc chute fins, wherein at least one of the fins comprises an angled leading edge; and a hermetically sealed chamber encapsulating the switch and arc chute assembly. 17. The contactor according to claim 16 wherein the angled leading edge of the chute fins is angled at about 30 degrees to about 90 degrees. 18. The contactor of claim 16 wherein at least one of the arc chute fins comprises a tapered body. 19. The contactor according to claim 18 wherein the tapered body of the chute fin tapers at an angle of from about 0 degrees to about 5 degrees. 20. The contactor according to claim 16 wherein the hermetically sealed chamber is pressurized with a thermally conductive gas, and wherein the gas comprises a mixture of hydrogen and nitrogen.

Inventors: BUSH BERNARD VICTOR, PRIEST MARCUS, REED J CLAYTON, BUSH, BERNARD, VICTOR, PRIEST, MARCUS, REED, J., CLAYTON
Applicants: BUSH BERNARD VICTOR, KILOVAC CORP, PRIEST MARCUS, REED J CLAYTON, BUSH, BERNARD, VICTOR, KILOVAC CORPORATION, PRIEST, MARCUS, REED, J., CLAYTON
Application year: 1998
Main classification: H01H9
IPC codes: H01H1, H01H9, H01H51