US2937256A - Contact structure for electric switches of the gas blast type - Google Patents

Description

May 17, 1960 P. BALTENSPERGER 2,937,256 CONTACT STRUCTURE FOR ELECTRIC swncuss OF THE GAS BLAST TYPE Filed Feb. 28, 1958 INVENTOR PCLUL Ball lensper-ger ATTORNEYS 1,937,256 CONTACT STRUCTURE OR ELECTRIC PFTH 'l PASITYPE Paul Baltenspe rger, Unterengsh'ingemnear Zurich, Switzerland, assignor to Aktiengesellschaft Brown; Boveri Qt Cia, Bade Swi erland; :io n es ock compa y alsificat n same as are new l r ority, application SwitzerlandMa'rdr-Q, 1 (a new) The present invention relates to electric switches the .air -bl ast type for. extinguishing alternating current particularly to switches wherein thesepa'ra "l8 contacts arecomposed of coairially arranged hollow ial i i i msmbs fih solid on act s a y in the form of a cylinder having a rounded head or nose a 'w sn' hsa a ts as es es U2 ration ofthecontacts, which is effected lat lve a1"movement'therebetween, the com se'd air dielectric, so t h'atre-ign ition between the contacts, after" the first zero ipassage of't'he alternating electric current.

being interrupted, is prevented to a great extent.

Iii all prior constructions for the hollowcontact ele.-

ment known to me, the configuration of the passageway fits into "and closes off an opening in the s arour id the head o'flthe solid contact intothe open} o h e same as been e er y that noz 35 Un d Pam' O 2 as high as possible and to increase, at the same time, t eins l ns stren th to su h an e tcnt. h t e hi vo a e esist e d t *has fi iss a t ta s. 80 a e ks 'w th se two u remen t t to a s tisfactory degree in switch constructions now being supplied to the industry.

I s. he efore, the object of the present invention to provide an improved configuration for the nozzle incorporated in the hollow contact which will serve to improve the dielectric strength of the contact zone during disconnectionof the contacts thereby lessening the chance form-ignition between the contacts and further to-decrease the splashing of metallic particles on the interior which has its most narrow cross-section in the w'cinity" of the contact plane with the rounded nose portion of the solid contact, the cross-section then progressively increasing in the direction away from the solid contact, i.e. in the direction of air flow through the hollow contact, thus to establish a nozzle effect intended to enhance the blasting action of the. compressed air.

The fact that the compressed air can enter the hollow contact only after the contacts have been separated has the result that no appreciable amount of air can flowv in the first moments ofcontact separation. For this reason, metal splashes can be thrown out by the arc and can become deposited on the walls of the extinction chamber or casing surrounding the contacts. Since such chamber is usually made of insulating material such as porcelain, the deposit of metal on the interior wall thereof undesirably lowers its insulating capacity. In order to avoid this, it has been proposed to so design the point of contact between the contact members that it widens only slightly, as seen from the contact point, and forms a narrow conical gap. This efiects a reduction in the ejection of glowing metallic particles but it cannot be prevented altogether. Besides, such an arrangement is possible oniy if thena'rrowest point of the nozzle is brought as close as possible to the contact point, to be able to make this gap as long as possible. At the narrowest cross-section of the nozzle, however, the pressure is lowest during the blasting, as known, so that the dielectric strength will also be lowest at this very point. Thus the amount of permissible recovery voltage is reduced. Such an arrangement is therefore not suited to meet the high voltage, high current circuit-opening capacity required of these switches in present day applications.

In order to obtain ahigh circuit-opening capacity, it is necess y to make the permissible disconnecting current around the solid contact which 4 7 art ofcontact se'paration, thej splashing of metallic partithe contacts. 1 Y In particular, the desired objective is attained byprofiling the interior passageway through the hollow contact to establish 'a nozzle in which the narrowest cross-section of the nozzle is so far away from the contact plane between the two contacts that the air pressure between the solid contact member and the place in the nozzle having the narrowest cross-section, at the instant of disengagement between the contacts, effects a sufficiently high dielectric strength with relation to, the recovery voltage. That is to say, the general configurationof the nozzle is thus, for example,- that of a Venturi comprising two truncated conical surfaces with theirsmaller ends in contact with each other. Moreover; the arrangement is such that the nose of the solid contact even though spaced from the area of minimum cross-section projects an appre extentintothe nozzle-like. passageway through the hollow contact that the latter formsa protective skirt prevents, at least at the wall of the insulator member surrounding and enclosing ,cl'es onto; walls of the surrounding insulating casing. This obtains when thetangent to the circular line of contact'hetween' the nose portion of the solid contact and the interior nozzle surface of the hollow contact extends through the lower skirt-like extension of the hollow contact which envelops the end portion of the solid contact.

The foregoing and other objects and advantages inherent in the inventive concept will become more apparent from the following detailed description with reference to a particular embodiment thereof and which is shown in the accompanying drawing, the single figure presented being a verticalview of the contact structure partly in elevation and-partly in central vertical section.

Wit-h referencenow to .theidrawing, the electric switch comprises a tubular insulator 1 through which compressed gas such as air is introduced in the direction ilb dicated by the arrows. However, no air flows until the hollow contact 2 and the solid contact 3 are disengaged by effecting relative longitudinal movement therebetween. This can be done in known manner by having the hollow contact stationary andthe solid contact movable, or vice versa. The arrangement can also be such that both the hollow and solid contacts move together in the first moments of contact separation before being disengaged.

As seen in the drawing, the interior of the hollow contact 2 which is formed as a surface of revolution, is shaped generally in the form a Ventun', there being an upper truncated conical surface section 2a joined at its narrow end along a line or plane 4 with a lower generally truncated conical surface section 2b. Thus, the passage way through the nozzle consisting of sections 2a and 2b has a minimum cross-section at the plane 4. The solid contact 3 has a nose portion 3a projecting into the lower nozzle section 2b and establishes a line of peripheral con tact with the surface of nozzle section 2b at the line or plane indicated at 5. Thus, as is evident, the contact plane 5 is disposed so far away from plane 4 designating 'ietsntssi M 7 960 3 v the point of minimum cross-section of the nozzle that an area of high pressure is formed in the nozzle section 2b between the planes 4 and 5 as well as between plane 4 and the end 8 of the nose portion 3a of the solid contact.

From the contact plane 5 which represents the greatest cross-section of the lower truncated nozzle section 211, the interior surface of the hollow contact curves outwardly and then downwardly to establish a skirt or screen" portion 6 which envelops a part of the solid contact 3 below the contact plane 5. The tangent to the contact plane 5 is indicated at 7 and it is seen that this tangent passes through the lower skirt portion 6 of the hollow contact 2.

Before the electrical circuit between the contact members 2, 3 is to be opened, the compressed gas such as air is present within the insulating casing 1 at the contacts. As soon as the solid contact member 3 becomes disengaged from the hollow contact member 2 at the contact plane 5, this compressed air flows around the nose portion 3a into the lower nozzle section 2b pushing the are formed between the contacts upwardly through the nozzle thus elongating and cooling the same, the arc being ultimately broken. Until the compressed air attains its full flow velocity through the nozzle, there is an interval during which metallic splashes can be formed. However, such splashes are now caught andretained by the depending skirt portion 6 and hence are prevented from reaching the wall of the insulating casing 1. The air pressure remains sufficiently high in the extinguishing position between the hollow and solid contact members since the point of narrowest cross-section of the nozzle is purposely located at line 4 which is sufliciently removed from the contact plane 5 to maintain high dielectric strength and hence prevent re-ignition of the arc between the contacts after the current has passed through the zero point in its cycle. Because of such construction, the improved switch is enabled to handle high disconnecting currents and with a high order of recovery voltage. Tests on the improved construction have indicated that the 4 disconnecting current can be increased by about 20% and the recovery voltage by about as compared with constructions which are now known.

In conclusion, it is to be understood that while I have illustrated one embodiment of the invent-ion, it is to be considered preferred rather than limitative and hence will permit of minor structural variations and configurations of contact design without changing the result and therefore will not depart from the spirit and scope of the invention as defined in the appended claim.

I claim:

In an electric switch of the gas blast type the combination comprising a hollow contact having a longitudinal passageway therethrough forming a nozzle and a solid contact in alignment with said hollow contact, said contacts being movable relative to each other in a longitudinal direction to effect engagement and disengagement therebetween and an insulator casing surrounding said contacts, the end of said solid contact being rounded and adapted to enter said hollow contact and engage the wall of said nozzle formed therein along a peripheral contact line therebetween, said nozzle decreasing in cross-section from said peripheral contact line in the direction of gas flow therethrough and having its minimum cross-section disposed remotely from said contact line, said hollow contact including a peripherally extending depending skirt portion completely surrounding the end portion of said solid contact and through which passes the tangent to said peripheral contact line, said skirt portion serving to intercept splashings from said contacts upon separation thereof and thereby prevent the same from reaching the wall of said insulator casing.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,673 Kesselring et al. Jan. 12 1937 FOREIGN PATENTS 639,566 Germany Dec. 8, 1936

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