US2515596A - Electric switch - Google Patents

Description

M. W. GRIFFES ELECTRIC SWITCH July 18, 1950 4 Sheets-Sheet l Filed Oct. 16. 1946 July 18, 1950 M. w. GRIFFEs 2,5l5,596

ELECTRIC SWITCH Filed o=. 16, 1948 4 SheetS-Sheet 2 INVENTOR. M11. razv W 'R/FFEJ /477'0 mw: YJ

July 18, 1950 M. w. GRIFFEs 2,5l5,596

ELECTRIC SWITCH 4 Sheets-Sheet 3 Filed Oct. 16, 1946 43 AffaAM/EVJ M. W. GRIFFES July 18, 1950 ELECTRIC SWITCH 4 Sheets-Sheet 4 Filed Oct. 16, 1946 INVENTOR.

M/L TON M GR/FFS BY Y M1) W TTORIYEY'S.

Patented July 18, 1950 ELECTRIC SWITCH Milton W. Grifl'es, Cleveland, Ohio,

asaignor to 'l'lle Electric Controller & Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application October 16, 1946, Serial No. 703,502 Claims. (Cl. 200-147) This invention relates to electrical current interrupters or switches. and more particularly to an electrical switch especially designed for interrupting altemating currents of power magnitudes and of relatively high frequency but usable also for interrupting alternating eurrents of the usual power frequeneies and direct currents as well.

Some form of magnetic blowout structure is almost universally used to assist in extinguishing the are or ares formed when an air-break switch opens a circuit carrying a current having a magnitude within the range commonly used by industrial apparatus, and, in the case of switches of the electro-magnetic contactor type, the blowout structure generally includes a blowout coil which is connected permanently in series with the stationary contact of the contactor so that all of the current flowing through the contacts while the contacts are closed also flows through the-blowout coil. No particular difiieulty is involved in the design of a permanently connected blowout structure that neither offers appreciable impedance nor heats -unduly when the switch carries -currents of the magnitudes commonly used by industrial apparatus and of a frequency in the neighborhood of 60 cycles, per second, but if the frequency of such currents is in the range of from say 200 to 10,000 cycles per second or higher, the impedance of the blowout coil and the heating thereof and of its associated iron structure is such that usual blowout practice cannot be followed. Consequently, conventional air-break, electro-magnetic contactor type switches which have permanently connected blowout coils and which are designed for interrupting alternating currents of the standard power frequencies, i. e. 25 or 60 cycles per second, are not suitable for interrupting alternating currents of the large magnitude and high frequency now commonly used, for example, to supply eoreless type induction furnaces or heaters.

Electromagnetic contactors for industrial control service and having continuous 230 volt ratings of the order of 1200 amperes or less at standard power frequencies have become very highly developed and standardized so that it is desirable to adapt such contactors for service in comparable power ranges at frequencies of from 2000 to 10,000 cycles per second thereby to make them suitable for controlling Induction heaters. Previous attempts to accomplish this result have involved the use of a means which short circuits the blowout coil during the closed period of the eontactor and which is operable shortly before openingof the main switch contacts to remove the short circuit thereby to render the blowout coil effective to assist in are extinguishment. In some instances the short-circuiting means is one pole of a triple-pole contactor and is connected in multiple with the blowout coi1 and the contacts of one of the other poles, the parallel combination being connected in one of the line conductors. The remaining pole, like the short circuiting pole, is not provided with ablowout coil and is interposed in the other line conductor. During circuit opening operation of such a contactor, the short circuiting pole opens first to insert the blowout coil into the circuit; the pole having the blowout coil then opens and the are is extinguished, and then the remaining pole opens to completely isolate the two parts of the circuit.

Another prior contactor type switch designed for high frequency service involves' the use of additional or areing contacts connected in paral- Iel with the main contacts of the switch and m series with the blowout coil so that the main contacts short circuit the blowout coil when they are closed. The main contacts of this latter type of prior contactor are arranged to open shortly before the arcing eontacts open thereby to cause the blowout coil to become energized just before and to remain energized during the areing period, the arc appearing across the arcing contacts only.

Both of the foregoing prior attempts to solve the problem of high frequency are interruption by modified standard low frequency contactors have required considerable redesign of the standard low frequency contactors, and have necessitated a predetermined sequence of contact opening which is difilcult to maintain. In both instances it has been necessary to derate the modified contactors considerably when used for high frequency service, and, in the case of the first described prior high frequency contactor, difliculty has been experienced because the last pole sometimes opens before the arc formed at the intermediate pole is completely extinguished thereby causing an are to be formed on contacts which are not in a blowout field.

An object of this invention is to provide an improved electro-magnetic switch capable of interrupting relatively large currents of relatively high frequency.

Another object is to provide an electro-magnetic switch for interrupting high frequency currents and which does not have the foregoing disadvantages.

atiaeoe Another object is to provide a switch for interrupting high frequency eurrents and which is essentially similar to commereially available contactors in so far as the prineipal-structural features are concerned.

While the improved eontaetor disclosed herein may be eonstrncted by slight modification of many eontactors now available commercially, the eontaetor disclosed in Trofimov Patent No. 2,071,595, issued February 23, 1937, is particularly well suited for this purpose and is the general type shown in the exemplary embodiments herein deseribed.

In aecordance with the present'invention, the blowout coil of a eontaetor type switch is so connected that it is completely isolated from the circuit while the main eontacts of the switch are closed, and is introduced for the first time into the circuit after an are is formed and has been transferred by thermal forces from one of the contaets to an are terminal receiving means in the form of an arcing plate. The areing plate is eleetrically connected to the movable contact through the blowout coil and through a pair of parallel connected are controlling conductors which are connected in series with the blowout eoil and disposed on opposite sides of the are path. The are controlling conductors not only serve as a path for current flowing through the blowout coil, but also are so mounted with respect to the are path that the current fiowing in the conductors tends to confine the are to a plane midway between the are shields, as in the above mentioned Trofimov patent. The blowout structure is so designed that the impedanee of the eoil is a minimum thereby to facilitate are transfer, but for interrupting currents having frequencies in the neighborhood of 10,000 cycles per second or whenever the are does not transfer readily from the moving contact to the arcing plate due to the thermal effect of the are itself, auxiliary means are provided to assist such transfer.

Switehes are known in which additional blowout eoils are added to a circuit in response to movement of an are across an areing surface, and in which the energization of a blowout eoil is inereased from a low to a high value consequent upon transfer of an are from a movable contact to a stationary arcing plate. However, these prior switehes are not suitable for high frequency service since they are provided with highly inductive magnetic means for effeeting initial are transfer and the impedanee of the blowout coils is made as great as possible so as to assist in reducing the are current. When the impedanee of the blowout coil is relatively large, some means must be used to assist the thermal effect in order to move the are to the stationary plate, and when this means is the usual blowout structure, the switch cannot be used for high frequency services. The present applieant has discovered that if the impedanee of the blowout coiI is kept as low as possible and the arcing plate is properly positioned' relative to the path of movement of the movable switch contact, that ares having a frequency as high as 6000 to 8000 cycles per second can be caused to move to the areing plate without the use of an auxiliary means.

It is a further object of this invention to provide a blowout structure for high frequency are interruption that is initially energized eonsequent upon transfer of the are from a contact to an arcing surface.

surface by the force of repulsion between the current in the are 'and the currentin an adjacent conductor.

Still another object is to provide an are eontrolling structure for an electric switch including means utllizing the force of repulsion between oppositely flowing eurrents in adjacent conducting paths to expand an are and to confine the are laterally to a pre-determined path and further including magnetic blowout means effective only after initial expansion of the are to assist in further expansion and ultimate extinction of the are.

Still another object is to provide an are controlling structure for an electric switch including means utilizing, the 'force of repulsion between oppositely flowing eurrents in adj acent corrdueting paths to move an are into a position in which it initiates energization of a blowout eoil by which the are itself is subsequently extinguished.

A more specific object is to so arrange the usuai fiexible conductor means leading to the movable contact of a clapper-type electromagnetie contactor that the current flowing through the fiexible conductor means serves to repel and expand an are immediately after its formation between the eontaetor eontacts.

Other objects are to provide a switch having a blowout coii of minimum impedanee that is energized only after an are is formed; to provide a switch having means in addition to a magnetic blowout structure for expanding an are, and to provide a switch having air-blast means for transferring an are from a movable switch contact to a stationary arcing surface.

Other objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

Fig. l is a circuit diagram;

Flg. 2 is a side elevation of a magnetic contactor in accordanee with this invention;

Fig. 3 is a front elevation of the eontaetor of Fig. 2,=portions of the' structure, at the left, being broken away;

Fig. 3a is a detail sectional plan view taken as indicated at 3a-3a on Fig. 2;

Fig. 4 is a perspective Vview of the eontaetor of Fig. 2 Vwith the air blast mechanism removed and the movable parts dropped to an abnormally open position;

Fig. 5 is a sectional view taken generally at 5-5 on Fig. 3, and

Fig. 6 is a detail view of an air blast generating mechanism of the switch.

Fig. 7 is a fragmentary side elevation of a eontaetor generally such as illustrated in Fig. 2, showing a modification of the invention.

Briefiy stated, the form of the present invention shown in the drawings eomprises an insulating base E0 mounting two identical pole structures H and i (Figs. 3 and 4) each of which has a pair of complemental contacts lt and i5 adapted to engage each other to complete a suitable electrical circuit therebetween. As shown in Fig. 1 by way of example, such a suitable circuit may c`omprise, for each of the pairs of contacts M and |5, a supply conductor lt extending from a source of altemating current G to an induction furnace F.V

Since the poles ll and l2 are identical and like see Fig. 2, flows through parts are referred to by the same reference numerals, the following will sufllce for both. Directly above the open contact i is positioned an arc terminal receiving means or arc-dissipating plate |8 having an inner end portion 18a (Figs. 1 and 5) of its lower or bottom face in close proximity to the vpath of travel of the top edge of the contact |5, while connected to and extending upwardly and rearwardly from the contact |4 is a generally inverted U-shaped conducting guard or arc-dissipating member IB. Between the front and rear walls of the member I!! is an arc-expanding means in the form of a blowout coil 20, a laminated, highly permeable core 2| of magnetic material surrounded by the coil, and a pair of laminated ear portions 22 of the core and of like magnetic material in magnetic flux conducting engagement with the core and extending toward and disposed on opposite sides respectively of the contacts |4 and |5. One terminal lead 24 of the blowout coil is connected to a lower terminal block 25 to which the contact 15 is also electrically connected as by a fiexible conductor 2G and a rocker arm 28. The other terminal lead 29 of the blowout coil is connected to a conducting U-shaped bracket 30 (see Fig. 3a) secured to the base IO and pivotally mounting, as on a pin 30a, a pair of conducting plates 3| to which the inner ends of a pair of conductors 32 are respectively connected. The conductors 32 constitute arcconstraining means as will hereinafter be described. The plates 3| are rigidly fastened as by a bolt dla to complemental arc shield members 34 of insulating material disposed on opposite sides of the contacts 14 and |5. The members 34 support the respective conductors 32 on curved ledge surfaces 34a formed on the outer surfaces of the respective members 34. The outer ends of the conductors 32 are connected to the plate [8, and, since the members 34 are disposed on opposite sides of the arc path, the conductors 32 are like- Wise so disposed. The contact l4 is mounted on the outer end portion of a conducting bracket 35 secured to the base |0 by a threaded stud 36 which is electrically connected, as by a bus bar 38, to an upper terminal block 39. The .arcdissipating member |9 which is also mounted upon the bracket 35 has its inner end insulated therefrom as by a fiber spacer |9a in order to prevent the completion of a short circuited turn about the blowout coil 20.

When the contacts |4 and |5 are in mutual contact, current reaching the switch through a conductor`31 and a lug 31a at the terminal 39, the bus bar 38, the stud 36, the bracket 35, the contacts l4 and l5, the arm 28, and the conductor 26 to the terminal 25 to which an outgoing conductor 43 is connected by means of a lug 43a. The blowout coil 20 is thus completely isolated and no heating of the coil 20, core 2 I, and/or ears 22 results even though the switch is carrying currents of relatively high frequency. When an arc is formed as at (Fig. 5) upon separation of the contacts |4 and 1,5, the

passes the irmer edge portion 18a of the plate |8 (broken line position l5x) one end of the arc transfers from the contact |5 to the plate 'IB as indicated at 42. It should be observed that the transfer of the arc may be obtained merely as a result of the thermal effects thereof and that the transfer is facilitated by the close proxdescription of one pole imity of the contact |5 and plate 18. Upon transfer of one end of the arc to the plate IB. the flow of current through the contactor is from the terminal 39 to the contact I 4, as before, and from the contact l4 through the arc to the plate 18, through the spaced arc-constraining conductors 32 in parallel, the plates 3|, the bracket 30, the lead 29, the blowout coil 20, and the lead 24 to the terminal 35. The blowout coil 20 is so wound that the magnetic field created thereby between the ears 22 in Vconjunction with the thermal effect of the arc itself causes th: arc to expand upwardly and outwardly away from the point of its inception as indicated at 44 and 4'5. In some instances it may be desirable to raise the respective outer end portions of the blowout ears 22 slightly from the position shown in order to concentrate the flux more closely to the arc during its period of expansion.

During expansion of the arc, one end thereof moves forwardly along the plate IB whereas the other end of the arc moves upwardly and rear- Wardlyalong the member IS. As described more in detail in the above mentioned Trofimov patent. the effect of the current flowing in the conductors 32 which, in the present invention, are energized as soon as the arc transfers from the contact |5 to the plate IB, is to constrain the arc to a position centrally of the spaced arc Shield members 34 and thus to confine the arc in the strongest part of the blowout field between the ears 22 as well as to prevent the arc from contacting and burning the arc shields.

In event that the contactor is to be used for currents of frequencies in the neighborhood of 10,000

48 through suitable tubes 5|. The nozzle is mounted beneath the contact Hi and the jet orifices 49 are directed into the arc path, i. e. upwardly and across the forward face of the contact S4.

Transfer of the arc from a movable contact to an arcing plate may also be effected i the force of repulsion between two adJacent curfiowing in opposite directions as will be described'hereinafter in connection with Flg. 7.

Having thus briefiy described the salient features of the invention, attention is now directe'd to the general construction and arrangement of the contactor hereof.

A cylindrical Operating shaft 54 rot'atably supported by a pair of spaced brackets 55 mounted by the panel IO has squared insulating tubes 56 disposed over opposite end portions thereof. Main contact arms 58 of the poles ll and 12, respectively, are secured to the outer end portions of the respective tubes 58 and a magnet arm 59 has opposing leg portions 59a (Fig. 3) secured to the inner end portions of the respective tubes 56. Considering one of the identical poles H and 12, the arm 58 thereof journals a shaft 60 to which the rocker arm 28 is keyed and which rotatably supports an intermediately pivoted, double-ended, adjustable stop member El. A compression spring 62, Fig. 2, interposed between the arm 58 and a lower arm portion 6|a of the stop member 6| is guided by a bolt 64 which passes sprawe freeiy through alignerlz openingsV inthe arm 88 and' the arm portion 8|a,,a' nut dla being threaded on the inner end portion ofthebolt. Thevspring 52: biasesthe member 8 I' clockwise'about the shaft 58 thereby forcing' an upper arm portion 81h of the member 64 against a flat surface 85 of the contact supporting' rocker arm 28. A pin 88 extends outwardly from the portion Glb, passes freely through an opening in the arm 28, and mounts a compression spring 88 disposed between the arm 28 and an adjustment nut 68 threaded, on the outer end portion of the pin. By means of'the construction just described the contacts ll and' 15 engage and disengage by rolling' action and are held in engaged position by adjustable spring pressure as is well known in the art.

Movement of the contacts I'S to engaged position is effected magnetically by attractive force between a magnet coreV 10, mounting" an Operating winding or coil ll, and a laminated magnetic armature 12 resiliently mounted. as by spring structures 'll on the magnet arm 59. In the embodiment shown.. the core 10 is laminated, has shading coils 15, and is secured to the base as by angle brackets 18. The coil 1| is provided with suitable terminal leads 18.

The magnet arm 59 has an upwardly extending portion 58b (Figs. 4 and 6) which, when the coi11| is de-energized, abuts against a stop plate 18 secured to and spaced from the, base |0 by a pair of elongated studs 8|. The blowout coil 20 may be of any type having suflicient turns to create an adequate blowout force, but, in order to have as low an inductance as possible, should not have an excessive number of turns. As shown, insulated round Wire is used for the blowout coil and is form wound in a double layer before being slipped over the core 2|, insulating discs or washers 84 being pro- Vided at opposite ends of the coil. The magnetic ears 22 are pivotally supported on a screw 85 passing through a triangular insulator 86 mounted on the outer end portion of the bracket 35 at the rear of the contact. ll'.

While the plate |8 may be a unitary piece of conducting metal, it preferably has a lower por- .tion i8b of insulating material extending over the major portion of the length of the plate, but

terminating to leave the conducting end portion contact.

Opposing marginal side portions of the plate l8 are received in grooves 88 formed in the inner wall surface of the respective arc shield members 34. The are shield members may be of molded insulation material and areheld together by the pin 31a to which the inner ends of the arc guiding conductor 32 are secured. Projections 88 formed beneath the grooves 88 on the respective members' 3| meet beneath the plate 8 to. space the members 34 apart and to assist in the support of the plate. I

Ef more positive. means than the thermal effect of the arc itself is desired for eifecting transfer of the arc from the contact to the plate |8, the non-electrical and non-magnetic arc transfer assisting means comprising the bellows 48 and nozzles 50 may be used. The bellows 48 comprises a fiexible plunger 80 (Fig. 6) mounted within a cylindrical container 8| which is fastened to the stop plate 18 as by a pair of screws: 821. A plunger actuating rod 84 secured to the base wall 88a of the plunger passes through aligned opening 95, 86 and 98 in a front wall 8|b'of thecontainer, in the stop plate 78, and in an S-shaped bracket 98, respectively. The bracket 88 is secured to the extension 59b of the magnet arm 58. When the magnet arm 59 moves to the closed position (shown in Fig. 6) the plunger 80 is compressed as a result of the pulling force on the rod 88 exerted by the braci-:et 88 against a nut 588 threaded on the end of the rod, air inside the plunger being discharged througha port. 9M in the wall 8lb. When the magnet arm returns to the open position, the plunger restores itself to its normal condition and forces air from the cylinder 8| through an outlet port E82' to a distributor lee. Because of the lost motion connection between the rod 84 and, the bracket 89, the magnet arm 59 reaches its open' position without interference from the red.

Air entering the distributor HM flows through the pair of outlet conduits 5d to the nozzles 5b of the two poles il and 12, respectively. The air is emitted from the nozzles through the orifices 49 concurrently with the formation of an are between the contacts H and IS. This puif of air assists the thermal effect of the arc and positively drives the arc upwardly so that the outer end thereof transfers from the. contact flrto the plate E8.

Referring to Fig. '7, the arc transfer may be effected by utilizing the force of repulsion between two adjacent currents fiowing in opposite directions, as mentioned. For this purpose a flexible conductor ll0, preferably uninsulated, comparabie to the conductor 26, and interconnecting a terminal block HI and the movable contact M2 is connected directly to the contact M3 through an elongated terminal tube or member l l3. The member Il3 is disposed beneath and in fairly close proximity to the are during the initial period of arc formation. The current in the are at any given instant is fiowing oppositely from the current in the member M3 and theiforce of repulsion between these two currents forces the arc upwardly and facilitates its transfer to the plate IM, comparable to the plate 88 heretofore described.

The fiexible conductor M0 is provided at its lower end with a terminal tube or member M5 electrically connected to the terminal' block iii and having its end portion bent at right angles to the portion adjacent the conductor M0; The upper end of the conductor ilu is received in the elongated terminal member M3 which is electrically connected to the movable contact M2 as by being clamped between the contact M2 and a rocker arm M8. The terminalimember M3 is preferably in the form of a fiattened hollow copper tube bent as indicated and extends rearwardly from the lower surface of the contact M2 toward an insulating base l l'l. The member M3 is of sufficient length so that it is disposed under the entire path of the initial arc drawn when the contact M2 moves from the solid line position to the open position shown by broken lines M8. 1 referably heat resisting insulation M8, such as glass tape impregnated with a silicone resin, be provided for the terminal member ll3.

When the movable contact M2 leaves the stationary contact l20, the current through the contactor flows from the stud E2! through the bracket 122, the contact l20, the are, the contact III, the terminal member I Il, the fiexibie conductor HO and through the terminal member 5, to the terminal block Ill. It is thus seen that the current in the arc is flowing in a direction opposite to the current in the member Ill. The force of repulsion between these two oppositely flowlng currents forces the arc upwardly and assists the inherent thermal effect of the heated are to cause the outer end of the arc to transfer from the contact ||2 to the plate ill, thus initiating energization of the blowout coil 123 which is the same as the blowout coil 20, and is connected in the contactor circuit in the same manner as the coil 20. The contactor of Pig. 7 is the same as that of Figs. 1 through 6 except that, instead of 'the air-blast producing means for initiating movement of the arc to the plate |8, the flexible conductor lu has been rearranged so as to perform this function, thus making possible more effective movement of the arc and simplification of the structure.

This application is a continuation-in-part of Iny copending application Serial No. 602,194, filed une 29, 1945, and entitled Electric Switches." now abandoned.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention:

i. A switch for opening and closing an electric oircuit comprising a pair of relatively separable contacts operative upon separation to form a gap between the contacts across which a current can normally flow as an arc, a conductor connected 'to one of said contacts and adapted for connection to one side of a circuit, the other of said contacts being adapted for connection to the other side of the circuit, an are 'terminal receiving means adjacent to said contacts, a hlowout coil connected between said arc terminal receiving means and said one of said contacts, and said conductor having a portion positioned relative to the gap between said contacts so as to conduct the circuit current past a sufiicient portion of the length of the gap, in adirection opposite to any are current between the contacts, at such proxirnity 'to the gap that the said current flowing through said conductor moves a terminal of the arc toward said arc terminal receiving means.

2. A switch for opening and closing an electric circuit comprising a stationary contact, a movable contact engageable with said stationary contact and sepai'abie therefrom to form a gap between the contacts across which a current can flow as an arc, a conductor connected to said movable contact and adapted for connection to one side of a circuit, the stationary contact being adapted for connection to the other side of the circuit, an arc 'terminal receiving means adjacent said movable contact, a blowout coil connected between said arc terminal receiving means and said movable contact, and said conductor having a portion positioned relative to the gap between said contacts so as to conduct the circuit current past a suhstantial portion of the gap, in a direction oppcsite to any arc current between the contacts, such proximity to the gap that the said current iiowing 'through said conductor moves a terminal of 'the arc on the movable contact toward said arc terminal receiving means.

3. A switch according to claim 2 further char- ````acterized in that means are provided for con- 0 straining to said position at least a portion of the conductor which is connected to the movable contact while leaving the movable contact unconstrained by the said means and conductor in its movement in the opening direction.

4. A switch according to claim 2 further characterized in that the conductor which is connected to the movable contact is fiexible and means are provided for constraining at least a portion of said conductor to said position during the existence of said gap.

5. A switch according to claim 2 further characterized in that the conductor extends entirely across said gap when the contacts are in their fully separated positions.

6. A switch according to claim 2 further characterized in that said conductor has a rigid conducting portion connected to the movable contact so as to be moved thereby to, and supported thereby in, said` position.

7. A switch for opening and closing an electric circuit comprising a pair of relatively separable contacts operative upon separation to form a gap between the contacts across which a current can normally flow as an arc, a terminal adapted to be connected to one side of said circuit, a conductor means connected between one of said contacts and said terminal, the other of said contacts being adapted for connection to the other side of the circuit, an are terminal receiving means adiacent to said contacts, a blowout coli, additional conductors connecting the coii between said arc terminal receiving means and said one contact, said conductor means having a portion positioned relative to the gap between said contacts so as to conduct the circuit current past the gap in a direction opposite to any arc current between the contacts at such proximity to the gap that the said current flowing through said conductor moves a terminal of the arc toward said arc terminal receiving means so as to reposition one of the are terminala thereon, whereby said conductors and blowout coil are energized through the repositioned arc, and said conductors being positioned so as to divide and conduct any current from the arc terminal receiving means past the repositioned arc in separate paths at opposite sides of the path of the repositioned arc in a direction opposite to the current of 'the repositioned arc such proximity thereto that the current flowing through said conductors constrains the 'repositioned are from lateral displacement.

8. A switch in accordance with claim 1 characterized in that said arc terminal receiving means is disposed above said contacts in the the r mal path of movement of the arc and in that said conductor is positioned below the gap so as to urge the arc upward to augment the thermal effect of the are.

9. An e'iectromagnetic contactor for repeatedly opening and closing a circuit carrying an alternating current, said contactor comprising a pair of terminals, a circuit of low inductance extending through said contactor from one of said terminals to the other and including an upper por- 'tion and a lower portion which is disposed directly beneath and in close proximity to at least a substantiai part of said upper portion, said upper and said lower portions defining opposing sides of the only loop in said circuit, a pair of separable contacts in said substantial part of said upper portion which when closed carry all asiasae ll of the current passing through said contaetor from one of said terminala to the other of said terminals and which upon separation while current is flowing therethrough draw an arc therebetween, said contacts being so disposed that said arc upon its 'initiation extends substantially in a horizontal plane at such proximity to said lower portion that the thermal effect of said arc and the. force of repulsion between the current in said lower portion and the arc current conjointly 10 cause a terminal of said arc to move upwardly along one of said contacts, an arc receiving means having an arc receiving surface elosely adjacent the upper portion of said one of said contacts and in the path of said upward movement of said terminal of said arc, an electrical connection between' said surface and the terminal to which said one contact is permanently connected, a blowout coil in said connection and of such low inductance that continued upward movement of said terminal of said arc causes said terminal of said arc to transfer from said one contact to said surface thereby to ener'gize said blowout coil. and the ilux produced by said blowout coil being so direeted that said arc is forced in the upward direction by said flux after said transfer.

10. A switch in aecordance with claim 1 characterized in that the said portion of the conductor extends across the entire width of the gap in all positions of the contacts.

HILTON W. 63m8.

REFEBENCES CI'I'ED The following references are of record in the flle of this patent:

UNITED STATES PATEN'I'S

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