US1799720A - Switch with magnetic blow-outs - Google Patents

Description

April 7, 1931. o. zlNGG SWITCH WITH MAGNETIC BLOWOUTS Filed April 28, 1924 Patented Apr. 7, 1931 UNITED STATES PATENT OFFICE OSKAR ZINGG, OF ENNETBADEN, SWITZERLAND, ASSIGNOR T AKTIENGESELLSCHAFT BROWN, BOVERI & CIE., 0F BADEN, SWITZERLAND SWITCH WITH MAGNETIC BLOW-OUTS Application led April 28, 1924, Serial No. 709,640l and in Germanyilay 14, 1923.'

Switches for direct current or alternating current, wherein the switch arc is, blown by a magnetic field, away from its point of origin and thereby drawn out, are frequently constructed with the switch contacts located between two pole plates and thus are located in a uniformvmagnetic field. The lines of force of this magnetic field' are approximately at right angles to the direction of 0 the currentin the generated switch arc, and the electric arc is thereby urged at right angles to its own length and at right angles to the direction of the lines of force, according to the well-known Fleming rule.

The effect of such arrangement is however greatly impaired or even annulled when the electric arc accidentally strikes at the edge of the contact surface instead of at the middle of the latter.' In such a case it is found in practice lthat the arc, owing perhaps to the high magnet-ic permeability of the'pole plates is urged, by its own magnetic field, beyond the edge of the contact surface and impinges against one of thepole plates or against the insulating layerv with which the pole plates are usuallycovered. Even with a single switching operation7 and, in any case, frequent repetition of this operation, a metallic deposit is formed on this insulating layer at theA pole plates. The electric are then extends only from each of the contacts to this metallic deposit. Themagnetic field between the pole plates is however incapable of exerting any effect uponthese remaining parts of the electric arc, because the current in these electric arcs flows in a direction parallel to the magnetic lines of force between the two pole plates. Consequently the electric arc, instead of being constrained to move and so become extinguished, remains in its place and destroys or damages the Switch.

Figure 1 is a diagrammatic drawing in plan of a magnetic blow-out device of known construction;

Figure 2 is a diagrammatic drawing in plan of a magnetic blow-out constructed in accordance with the present invention;

Figure 3 is a diagrammatic elevation of a pair of contacts and a blow-out device constructed in accordance with the invention and comprising a pair of energizing coils;

Figure 4 is a plan view of the arrangement shown in Figure 3;

'Figures 5 and 7 are elevational diagrammatic views of further modifications or arrangements according to the invention;

Figure 6 is a plan view of still another modification.

In Figure 1 o; are the contacts which are being drawn apart in the direction of the arrow w; b is the electric arc that is formed between them; c are the pole -plates between which the magnetic field is indicated by the lines of force shown furnished with barbs. This magnetic field has the direction indicated by the barb on the axis y in Figurel and exerts u on the electric are b, in which a current is owing in the direction of the barb on the axis a force in the direction of the barb on the axis a, that is to say, perpendicular to the plane of the drawing. When,however,the electric arc strikes at the edge of the contacts (electric arc b) and impinges upon the pole plates c, it consists substantially of two portions flowing in the direction of the arrow y, and one portion flowing in the direction of the arrow a' which latter, in some cases, may no longer exist as an electric are, but passes away as a line current in ametallic deposit.

Under such conditions the arc portions extending between the edges of the contact members a and the adjacent pole plate c are parallel to the lines of forces of the magnetic blow-out field. As a result, no force will be exerted between the field and the arc, leaving the latter stationary at the point where it started, with entire loss of the blow-out'effect gimed at by the provision of the magnetic eld.

The present invention has now for its object to provide an effective means for obviating that drawback of the usual arrangement, said means consisting in providing gaps in the pole plates over the place in which the switch are is formed. The resulting arrangement is illustrated in Figure 2. In this figure, a are the contacts which are being drawn in the direction of the 'arrow b is an electric arc which has struck on the edges of the contacts and has thereby been deflected up- Wards. c are the pole plates which, in this case, are gapped at the place above the contact surfaces. The electric arc isnow unable to impinge upon the pole plates, and there-` fore all the magnetic lines of force intersecting the electric arc remain eifective. The magnetic force exerted upon the electric arc by the magnetic field is now not limited to that portion fof theelectric are fionf'i-ngin the direction indicatedbythea-rrow a?, butit also comprises chiefly the portionsflowing in the Y direction indicated by the arrow y; these 'latter portionsare hereinafter jreferred, `to-,as the are terminal or foot ofthe electric arc. The

reason 4forthis is that, in this improved Larrangement, themagnetic lines of force .do not have the sameV direction as the arrow y, but have, at the place referred to, also ,a compo- 4'nentxhavingthe direction ofthe arrow'm, so that these lines :of :force intersect-the portions of the electrica-rc that kflow in :the direction .findicated'by the arrow-y. Itis this force, exerted upon the foot of the electriciarc, which I ,produces the lmost effective movement fof the electricarc.

.In manycases itis desirable toemploy only lone exciting coil Vfor `theinagnetic .bloiv-cut ifield. In suchiafcase, accordingztothis invention, integral pole plates slotted over the contact place may be employedfor both switch contacts. o

yIn other cases, where less :importance is lplacedu'pon the .employment ofonly one/#ex citing coil, v.an additional and particular `advantage i can -be gained,y Vaccording'fto this inrventi'on,:by. providingseparatepole:platesfor each switch contact, because in such fca'ses it Yis not necessary .to insulate the pole plates fromithe contacts. Onthef'contrary, theipole plates .may be connected directlyito :the contact pieces byy screwsfor yothermeans. In this mannerzthe distance between :the .pole plates may be made as small "as possible. `The required number of ampereeturns, zandV therefore ;-the dimensionsnf theiexciting coil are diminished to such 'a degree :that'theitwofexyciting coils required fortwo contacts are'toigethergenerally not larger than the-common Vexc'itingfcoil Vin 'the case of iintegral pole plates.

The arrangement described-with reference to Figure 2,'has theadvantage that, even .if ftheelectricarc strikesat the edges of the'contacts, it will be driven further away by :the magnetic y'field and extinguished. In' some cases however it may yremain,fpermanentlyat the edges of the contacts,lor-atthe edges of Ythe arcing horns connected to-thesecontacts,

"f vso that,especially .with pole Aplates `mounted Without insulation, vthere .is the irish that the electric arc will overlap the pole plates and damage them. It -is ktherefore desirable lto move the electric arc, vbymeans offthe mag- ,netic.field, in sucha imanner that,even when tions, ywherein, in Vagreement withthe' Areferences used in connectlon with Figures l and 2,

Figure 3 is a view in the plane m-e taken along 'the direction of the axis y, and

.Figure 4 is a viewin the plane.m-y, taken along the direction of the axis 2Q n .In these figures, :as before z-a are fthe contact Vpieces is ,the electricfarc care `thegpole -platesycl arethe magnetcores; e arefthc exciting coils, one for each pair fof -pole plates,

ythat is to say, ,for :each fcontactz; farefthefarcying horns,the surface o f which, shown in lFig- `ure kil, constitutes the farcingfpath.

The pole plates arescrewed'directly'.tofthe arcing horns :without the interposition` of .an

linsulating layerV at -thegplaces marked ig. `The Yarcing path includes, with gthe contact V.surface, on which the contacts acome incontact :with one another,anfangle whichisnssumed here to bearight angle. y

VThe operation yofwthis -arrangementfwill be `'clearly understood `vfrom ,inspection of :the

`magnetic .lines offforce ywhich are represented Yin 1Figure '4 fby thin 4lines furnished with barbs. ,The magnetic lines of force are curved throughoutthe entire-space wherein tithe ,arc :may be started, or `vbe 4moved onqthey contact kmembers a,:.thatfis, on thefportionsfof theconftactmembers which are inengagement with --each other When the circuit is .closed,iaswell as cnithee-side vedges'of said contact members and von tthe :top thereof. The 'curved magnetic lines of iforcefresulti'ngpfrom the'gforefgoingarrangement "of the ipole plates with :respect tothe contact members, will, vaccordingly, always Ahave a lcomponent :in ftheadirecf center fof the lattenmSolongas theielectric arcis situated linathe position shown .'infFigures `1 IandQ, it VWillfbeacted upon, as above stated, onlyfbyiforces havingthe direction of the axis e.r :Whem however,ithefelectricarc lis caused, Yby "the blowing action `Iof they maginetic field, to passsout ofthe space included ki between fthe contacts, Vand 4assume theposition shown in Figure A,3,1the current-.1n gthe kfoot ofthe electricrarc will floWin-thedirccltion'ofthe axis '2.

The foot of the electric arcfreceives thus,

from fthe magnetic field component having fthe'direction offtheaxis fr, lanurge in thedirection of--the arrovv,.1/,.tovvards thevmiddlerof the arcing.` path. If theelectricarchas struck at the-edgesof the fcontactsit will there`fore A :tion of the 'axis Y00,-;or yin generahfso .directed Y :asito :causethe'arc to fbe :driven upwarchand :then along the `arcmg `horns gf, "towards Vithe follow the path indicated in Figure 4 by the long-dotted line This path is, at all points, atA right angles t0 the projection of the magnetic lines of force shown in Figure 4, and it reaches the centre line of the arcing path quite near the point where the electric arc passes round the corner of the contact piece a from the contact surface on the arcing path. Experiments made with such switches have shown that this action occurs quite regularly, so that after repeated switchings, the arcing path surface situated between the two lines z' in Figure 4 appears to be sown with traces of the electric arc, whereas no such traces are to be found outside the lines i.

The urge with which the electric arc, after passing the corner between the contact surface and the arcing path, is driven towards the middle of the arcing path, may be further increased, according to this invention, by setting the edges of the pole plates back from the arcing path, and bringing the said edges nearer to the arcing path in the direction of the movement of the electric arc.

A constructional example of this arrangement is illustrated in Figure 5 wherein the reference letters have the same significance as in the preceding figures. The magnetic lines of force acting vupon the arc terminal or foot of the electric arc extend, in this case, in planes which are situated at right angles to the edges of the pole plates, that is to say, which enclose an angle a with the l1/--2 plane. a is also the angle between the edges of the pole plates and the arcingtpath. The magnetic lines of force, therefore, here also have a component in the direction of the axis m, namely along the entire stretch along which the edges of the pole plates enclose the angle a with the arcing path; in some cases, therefore along the entire arcing path. The force which has a tendency to drive the electric arc to the middle of the arcing path is therefore, in this case, not limited only to the corner between the contact surface and the arcing path, and their immediate proximity, but occurs also in the further advance of the electric arc, although to a less extent.

A further means for achieving the same end consists, according to this invention, in that instead of arranging the pole plates parallel to each other, they are arranged to converge together in the direction of the movement of the electric arc in the manner illustrated by way of example in Figure 6. This arrangement has the eect of causing the magnetic lines of force to have components in the direction of the arrow a at the places above referred to.

In both arrangements shown in Figure 5 and Figure 6 it is not necessary that the inclined position of the pole plates or of their edges relatively to the arcing path shall extend over the whole length of the arcing path. This inclined position may be provided only here and there, and in some cases may be repeated in several places. An example of such an arrangement is illustrated in which the edge of the pole in Figure 7 plates has a serrated formation.

' In the switches or circuit breaker devices described hereinabove, I have thus combined a number of features which greatly improve the blow-out action exercised by the Inagnetic ield on the interrupting arc incident to the opening of a. circuit. By setting back the edges of the pole plates behind the ends of the contact surfaces of the arcing contacting members a the magnetic field in the vicinity of the arc terminals is given a shape as to positively secure arc movement in the direction towards which it is to be blown independently of the point where the arc has been started, whether in the middle of the contact members, or towards the edges thereof. The provision of a magnetic blow-out mechanism in which a distinct set of pole plates is associated with each of the contact members, and so arranged that the two sets of pole plates are substantially in contact with the associated contact members, but the two sets are insulated from each other, with a gap between the two sets of pole plates at the points where the arc is started, secures not only the above mentioned improved blow-out action, butalso solves the many diii'iculties incident to the proper insulation of the contact members with respect to the pole plates, so as to secure satisfactory opening of the circuit and avoid bridging of the contact members by a deposit of conducting particles on the walls of the closed arc chutes in the prior art constructions. i l

The shaping of the contact surface of the arcing members and of the adjacent surface of the arcing horn, by bending the path of arc travel, secures, in conjunction with the offset magnetic pole plates, definite upward movement of the arc terminal from the point where the arc was started, and in the course of the further travel thereof, its movement towards the center of the arc travel surface on the arcing horns; the inclination of the edges of the pole plates to the surface of the arcing horns and the greater spacing between the pole plates near the starting point of the arc than at the further removed points of the arc horns, still further increases the directional control of the arc movement over the entire path of its travel.

Switches constructed according to the present invention are distinguished above all by their very compact design. They are suit- 'able for use as elements for controllers and similar apparatuses comprising a plurality of switch elements, and especially for use with high voltage current on account of the possibility of dispensing with the insulation of the pole plates.

lli)

While onlythe switch contacts a andthe :various parts or elements immediately assov -ciated therewith have been shown and .de-

scribed, Eit will be understood that the .varions other partsof the circuit breaker, such as the supporting .members for 4the contacts andtheniechanism foi-.effecting movement of lthe same vinto vand out-of contacting relation, may be of any suitableconstruction, such as lis found in the usual circuit .breakers of this general type.

VV- hat I claim is:y

.1. In a circuit brealrel1 device, a pair v ofsepvarable arcing-contact members, an arcing Yhorn extension member associated with each l, of saidcontactmembers, and a magneticblowout-device for causing the arc drawn between said contact members to travel i.nto 4the space between said horn extension :members and .comprising a pair of `pole-.shoe plates disfposed adjacent to oneof said contact Vmem- -bers,ysaid pole plates havingedges setbaclrof .the edges of the contact Vsurface ofsaidcon- .tact member andconvergingtowardsthe edge Iofftne surface of travel of said arc on the asrsociated horn extension member,.and l.means for inducing a magnetic fiuX taking a curved path Afrom the edge of the' pole-shoe plate lononeside of a contactmember, over the surface of travelof thearc terminal on said contact ,member and the arc-horn extension, :to- -wardthe correspondingn edge of the .pole-shoe plate disposed on Vthe other sideofsaid contact member.

`2. VThe combination Iwithacircuit breaker .having Ya ,pair .of separable arcing contact ,members and an arc-travel .path towards 4.which the .arc drawn .between said .contact members is blown, of a magneticblowfout de-. -viceoperable toL cause the` arc .to travel Valong vsaid path and comprising a pair of .pole-shoe plates having pole surfaces converginginthe directionrof--the arctn vel along saidpath.

3. The combination with a circuit breaker comprising a pair of separable arcing con- ;tact `members and horn extensionsassociated .witheach of saidcontact members,;of armag- 'fnetic'device `for blowingthe arc between said rand the associated horneXtension, said .pole- 'name yto this specification.

said horn extensions, said device comprising a pair of pole-slioe members extending on both sides of one of said vcontact mem'bersand.

the associated liornextension, said pole-shoe members having magnetic pole surfaces set back ofthe edges'of the surface of travelof the arc terminal onsaid contact member-and .said l.horn extension, said pole surfaces converging towards eachother in the direction Aof the arctravehthe pathofarc travel. onsaid ,horn extension being inclined` to the contact surface between said contact members.

Aportions .adj acent said contact toward their votherend portions.

6. In an velectric switch with:v magnetic blow-out apparatus `confiprising switch con- .tacts Alocated between pole plates, .the plates beinggapped in the regionof `the initial arc and arranged to form an angle with .the plane .of movement of the .arc and approaching the plane in the ydirection of the rmovement/vof.the

arc root. Y

7. In an electric switch with magnetic blow-out apparatus comprising switch lcontacts,lpole platesarrangedalong the sidesof Asaid contacts, said pole plates being gapped in the .region o fzthe initialarc formedduring a switching` operation,and arcinghorns along which .the arc travels, said pole plates being arranged to approach said'liornslin the direction of travel of the arc andfdefininganfalcing path therewith, said `horns being so located relative to the arcing path as to include angles yformed by said pole plates with said switch contacts.

In testimony whereof I have signed my OSKAR ,ZINGGL

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