US2337495A

US2337495A - Circuit interrupter

Info

Publication number: US2337495A
Application number: US357393A
Authority: US
Inventors: Herbert L Rawlins
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1940-09-19
Filing date: 1940-09-19
Publication date: 1943-12-21
Anticipated expiration: 1960-12-21

Description

Dec. 21, 1943. H. L. RAwLlNs l CIRCUIT INTERRUPTER.

` Filed sept. 19, 1940 INVENToR HORN H e rberz L Fa w/fm.

wlTNEsSEs:

Patented Dec. 2l,

2.337.495A CIRCUIT maxaman.

nennen L. Rawlins, wilklnsbnrg,

Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of .l v Pennsylvania Application September i9, 1940, Serial No. 357,393

' (Cl.- 20M-120) 34 Claims.

This invention relates generally tocircuit interrupers, and more specically to interrupters which are capable of automatically interrupting a circuit in response to the passage therethrough of currents above a predetermined value, vand at the same time limit the value of the current inter- -`rupted. 'I'he invention will'be more particularly disclosed in connection with a fuse which is capable of limiting the current when the fuse blows.

In order to limit current in a fuse to a value substantially smaller than the normal short circuit current, it is necessary to introduce a resistance or impedance within the fuse which is large compared to the impedance externally oi the fuse. Such aresistance may be provided in the arc formed when the fuse blows, or the curand arranged so that when an arc is struck at said arc establishing means, the current is/substantially instantaneously shifted to said current limiting means.

A further object of this invention is to provide a circuit interrupter having means to establish an arc in an arc restrictingl passage, with current limiting means in parallel with said arc establishing means.

A further object of this invention is to provide circuit interrupting means having meansl for automatically interrupting a circuit in response rent may be forced to flow through a current limiting means in the fuse at the time of interruption. Resistance may be provided-in the arc by restricting or confining the arc to raise the arc voltage. This method ofl limiting the current however, has certain disadvantages in that restriction liberation and destroy the'arc boundary walls, and hence render control of such an arc extremely dimcult. surges that occur during the operation of fuses of this type, may also be so severe that flashovers vwill occur on adjacent apparatus.

of the arc may result in excessive energy 'to curnnts above a predetermined value and shift such currents to current limiting means in shunt relation thereto, with additional vmeans for au tomatically interrupting a circuit in response to currents above a in series circuit relation with said current limiting means.

Another object of this invention is to provide acurrent limiting fuse having fusible meansin a restricted passage in parallel with current limiting means, and other fusible means in series with said current limiting means.

The resulting arc voltage or voltage Another object of this invention is to provide a-novel type, of current limiting fuse embodying a plurality of fusible means and current limiting means all arranged in a single structure in a novel manner.

In view of the foregoing. it is preferable to s limit the current by causing it vto flow through a current limiting means within the fuse. However, since it would not be desirable to provide a current limiting means such as a resistor in series in the circuit, it is necessary to provide a 4shunt circuit around the resistor, which, when the current rises above a predetermined value, will' open very fast to shift the' current through the lresistor to thereby limit the current. It is desirable that the current be shifted to the reslstorias rapidly as possible, preferably within a fraction ofa half cycle, so that the resistor may be'eifective to limit the current. i

This invention will'be hereinafter particularly disclosed in a current limiting fuse of the lastmentioned type, and one object of the invention is to provide a current limiting fuse which is capable of functioning to interrupt a circuit in response to currents above a predetermined value, and which is also effective to limit the value of such currents.

A further object of thisinvention is to provide a circuit interrupter having arc establishingmeans in parallel with `current limiting means Another object of uns invention is to provide a novel fuse having a resistor element Vfor both limiting vthe current and heating a fusible means in a novel manner. i i

Another object of this invention is to provide a novel'c'onstruction of a time delay fusible circuit interrupter. I

Still another object of this invention is to provide a circuit interrupter of a novel construction embodyingreadily visible indicating means to invdicate the open and closed circuit conditions of the interrupter.

These and other objects of this invention will i become more apparent upon consideration-of the following detailed description of the preferred embodiments thereof, taken in connection with the attached drawing, in which: l y

Figure 1 is a longitudinal cross section view of a current limiting fuse-embodying the principles ofthe invention: and

Fig. 2 is a longitudinal cross sectional view of a modified form of fuse embodying some of the parts of the fuse shown in 1.

Referring tothe drawing, in Figure 1' there is t shown a fuse including a fuse tube 2 of insulat ing material which is preferably .a transparent predetermined value arrangedy upper terminal cap coil tension spring 26 in a similar manner.

' through spring I6.' fuse insulating material such, for exampl a transparent resin. The fuse tube with metal endterminal caps 4 and 8' for the opposite ends thereof respectively, and these terminal caps are secured to the ends of the fuse tube by a plastic material 1 provided between the cap flanges and the tube. Within the fuse tube 2 and seated against the terminal cap 6, there is provided an insulating rod 8, which may be of any desired insulating material, preferably an insulating material which is capable of evolving an arc extinguishing gas to an electric arc, a synthetic resin. The insulating rod 8 is provided with a relatively small central bore III which is of substantially the same size as a fuse wire I2 adapted to be positioned therein, and preferably the bore I has a diameter of h inch or less, its minimum by the size of fuse wire I2, all for a purpose to be hereinafter referred to.

The fuse wire I2 may be of any desired fusible resistance material such, ogpcopper alloys. and the lower end thereof extends through an opening in the end cap 8 to be soldered to the end cap as, solder I4. The other end of fuse wire I2 is secured to one end of a coil tension spring It, as by soldering or the like. Coil spring It is tensioned and the other end thereof is extended through-anaperture in terminal cap 4, to be bent over and secured to the end cap, for example, as by solder Il. As shown in Fig. l, the upper end of bore III through the ulating rod l is enlarged to receive an insulatin sleeve of fiber or the like, which is positioned between the bore I0 and 4, about coil tension spring as glass or 'posluoned between the insulating .ueeve zo and fuse tube 2, there is an annular current limiting element 2I, preferably a non-metallic resistance material such, for example, as carbon or the like. The resistor element 2| is confined between end cap 4 and a conducting metallic washer member 22 seated on the lupper end of insulating rod 8. As shown in the drawing, insulating rod l is substantially smaller than the interior diameter of fuse tube 2 so as to provide an annular space therebetween. In this annularspace there is provided a second fuse wire which preferably melts at a lower current than does fuse wire I2, and which is capable of melting substantially instantaneously in response to predetermined conditions. Y

In order to obtain substantially instantaneous fusing of fuse wire 24, which should occur in less than a half cycle, this wirevis preferably made of silver or a material having similar characteristics. The fusev washer 22 as by soldering or the like, and to a The coil tension spring 26 is provided with relatively large coils which lie in the annular space be tween fuse tube l2 and insulating rod 8 and the spring -is tensioned with the lower end thereof extending through a second aperture in terminal cap 0 and bent over and secured thereto, as by solder 28 or the like.v

It willv now be apparent that in the structure in Fig. l of the drawing,.there are provided two current carrying paths'in parallel through the fuse. One path extends from terminal cap 4, wire I2 t0 end cap l. the fuse extends from 2l, conducting washer The other path through terminal cap 4. resistor 2 is provided wire 24 is secured to conducting when in proximity such, for example, as fiber or dimension being limited only for example, as silver for example, by the 26. The use of a small arc established by Vspring 28. The

assmas 22, fuse wire 24, and coll tension spring 26 to end terminal cap 6. Obviously, since the latter path includes the resistor 2| during the normal unfused condition of the fuse, the greater portion of the current will be carried by fuse wire I2 and substantially no current will pass through fuse wire 24 and resistor 2i.

In the operation of the fuse illustrated in Fig. 1, upon the occurrence of heavy overloads and overloads on the order of short circuits, fuse wire I2 will be melted or will soften to such an extent as to permit coil spring I6 to insert a gap in the circuit and draw an arc in bore I0. Bore IU. however, is so small appears across the bore, the current will be substantially instantaneously shifted to the parallel circuit through resistor 2|, fuse wire 24 and coil viously stated, to melt substantially instantaneously preferably within a fraction of a half cycle, on any current capable of melting fuse wire I2, as limited by resistor 2|. It will be apparent, therefore, that fuse wire 24 having a lower melting point than fuse wire I2 will accordingly melt at lower currents than fuse wire I2. As soon as the current shifts to the parallel circuit through resistor 2|, it will be limited thereby, and the current thus llimited will melt fuse wire 24, and this limited current arc is drawn out and easily extinguished in the annular slot between fuse tube 2 and insulating rod I. by coil tension spring bore I0 to restrict the fusion of fuse wire I2, is esto instantaneously provide a high arc voltage to substantially. instantaneously shift the current from bore I0 to the parallel circuit through resistor 2I and fuse wire 24. v

The word instantaneous" or term "at the same instant as used herein and in the claims to indicate the time of operation, denotes a time of considerably less than a half cycle of a 60- cycle wave, and preferably a small fraction o1.' a half cycle onA the order of a few hundred microseconds.

. It will be noted that by virtue of its connection to conducting washer 22, the fuse wire 24 is thereby placed in conducting relation with respect to resistor 2I. This is important in the event fuse wire I2 is blown and the current drops before fuse wire 24 blows. Buch a condition pecially important might occur on relatively light overloads, and in this event the heat generated by resistor 2l will be suillcient to melt fuse wire 24 and interrupt the circuit. Inasmuch as insulating rod 8 is of a material Iwhich is capable of evolving an arc extinguishing gas when in proximity to an electric arc, this action, both with regard to an arc struck in bore III, or in the annular space be tween rod 8 and fuse tube 2, will aid in extinguishing these arcs. With respectto arcs struck in bore Il, the arc `extinguishing action of gas evolved from linsulation I will decrease the time required to transfer the Acurrent to the parallel path through resistor 2l and fuse wire 24, and

with respect to arcs struck in theannular space between insulating rod l and fuse tube 2, the action of arc extinguishing gas evolved from insulating rod I aids in more quickly interruptmg the circuit.

It should be noted that two stressed fusible means are provided in parallel relation in a single fuse cartridge together with a current limiting means, and that the fusible means for finally interrupting the circuit is provided'in an annular slot subject to the action of an arc exthat as soon as arc voltage fuse wire 24 is designed, as preassigns tinguishing gas. The arc passage in the form of an annular slot is advantageous inasmuch as the arc is thereby deformed, and made to conform to the shape of the passage, and this raises the arc voltage while at the same time causingl the arc to contacta greater surface of the gas evolving material, and both of these actions .together with attenuation of the arc by coil spring 26 provide a combined action on the arc to quickly extinguishl the same and thereby interrupt the circuit. l 4

In Fis. 2 there is shown a modified form of fuse embodying many of the features of the fuse shown in Fig. 1, and therefore, like reference v numerals will be used to designate like parts. The fuse shown in Fig. 2 is substantially identical with that illustrated in Fig. 1, except that the insulating rod 30 within fuse tube 2 is solid, and the fuse wire I2, bore I0, and coil spring I8 are thereby eliminated. A solid block 32 of a resistance material which may be of the same material comprising located between upperterminal cap 4 and conducting washer 3| and in contact therewith. A

There is but a single circuit through the fuse slown in Fig. 2, and this l terminal cap 4 through resistor 32, conducting washer 3|, fuse wire 24, coil tension spring- 26 to end terminal cap 6. It can therefore be seen that 'the fuse of Fig. 2 embodies a resistance which is always in the circuit. and thereby serves `to not only limit the current through the fuse,

but also to heat fuse wire 24 on light continuing overloads to obtain a desirable time lag onthese overloads, in the blowing of the fuse. On relatively high currents, such as short circuit cur,- rents, of course, the fuse wire 24 will melt sub;

stantially instantaneously andL thereby interrupt the circuit faster on such overloads than on relatively light overloads. When the fuse wire 24 melts, of course, coil spring 26 is free to move .towards terminal cap 6 and thereby draw out and elongate the arc to extinguish the same in the same manner described in connection with the fuse shown in Fig. 1.

In connection with both embodiments of this invent-ion, it is apparent that the transparent fuse tube 2 will render the coil spring 26 and fuse wire 24 visible from -the exterior and the condition of the fuse may be thereby readily ascertained.

In the foregoing there has been disclosed novel forms of fuses, one of which embodies current limiting means which is normally outside of the circuit through the fuse, but which acts to carry the current through the fuse in, response "to currents above predetermined values determined by a fuse wire I 2; 'I'he current transfer from fuse wire I2 to the resistor or current limiting means is effected by the provisionof fusewire l2 in a parallel circuit, and in a restricted arc bore, to

' thereby obtain a high arc voltage when the fuse wire melts and effect a quick transfer of the current to the current limiting means. In both forms of the invention a current limiting means in the form of a resistor isemployed which isI in heat conducting relation with respect to a fusible element to thereby insure blowing of the fusible element, and interruption of the circuit in the embodiment of the invention shown in Fig. 1, and to lProfvide a time delay in the blowing of the fuse in the embodiment of the invention shown in Fig. 2. These and the other features of the invention'disclosed herein have `been em-y bodied in a particular type of apparatus wherein resistor 2| shown in Fig. 1, is

extends from upper A 3 they find particular novelty of cooperation land utility, it should be noted however that these features are also usable in connection with other types of fuses and circuit interrupters.

Although the resistance element in the embodiment of the invention disclosed herein is referred to both here and in the claims as cur` rent limiting means, it is apparent that the high arc voltage, which occurs instantaneously upon fusion -of thefusible element shunting the resistance element, will limit the rise of current prior to its transfer to the resistance element, and thus exert an initial current limiting effect. The resistance element is effective as soon as transfer of the current to it occurs, to limitV the current to a predetermined value, and this current is then finally interrupted by theA series fuse element at the first current zero. The instantaneous transfer of current to the resistance element will, obviously, also limit the voltage to a value determined by the current flowing through the resistance element.

Having described lpreferred embodiments of lthe invention in accordance with the patent statutes, it is desired that theinvention be not limited to the particular embodimentsV disclosed, inasmuch as it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in these' particular structures without departing from the broad spirit and scope of this invention. Therefore, it is desired that the invention be interpreted as broadly as possible andthat it be limited only by the prior art and by what is expressly set forth in the following claims.

Iclaim as my invention: v

l. In a fuse including a tubular fuse holder hav ing terminals adjacent opposite ends thereof,

fusible means and current limiting resistor means in said holder and connected in series between said terminals, additional fusible means in said holder in shunt relation 'with at least said resistor means and located in a long, narrow, arc restricting insulating passage having solid walls, and said passage being sufliciently long and narrow as to cause the voltage of an arc struck therein to rise instantaneously to a value at which the current will beV transferred to the shunt circuit com`= prising said resistor means and said first-mentioned fusible means. i

In a fuse including a tubular fuse holder havingv terminals adjacent opposite ends thereof, fusible means and current limiting resistor means in said holder and connected in series between said terminals, additional fusible means in said holder in shunt relation withat least said resistor means and located in a long, narrow, arc restricting insulating passage having solid walls, said passage having at least inner wall portions threof of a material capable of evolving an arc extinguishing gas when in proximity to an electric arc, and said passage being'suiiiciently long and narrow as to cause the voltage of an arc struck therein to riseinstantaneously to a value at l which the current will be transferred to the shunt circuit comprising said resistor means and said first-mentioned fusible means.

3. In a fuse including a tubularffuse holder ihaving terminals adjacent opposite ends thereof,

fusible means and current limiting resistor means in said holder and connected in series between said terminals, resilient means biasing a terminal of said fusible means to elongate the arc formed upon fusionV thereof, fadditional fusible means in said holder in shunt relation with at least said Y means in said passage and resister means and independently located in a long, narrow, arc restricting insulating passage having solid walls, and said passage being sufiiciently long of an arc struck therein to rise instantaneously to a value at which the current will be transferred to the shunt circuit comprising said re sistor means and said first-mentioned fusible.

means.

4. In a fuse, a fuse tubeof insulating material having terminals adjacent opposite ends thereof, means of insulating material in said tube and spaced from at least a portion of said tube wall to form an arc passage in air therebetween, said means of insulating material having a bore therethrough, separate fusible means in said bore and passage, respectively, said fusible means connected ing means connected only between said fusible one of said terminals.

5. In a fuse, a fuse tube of insulating material having terminals adjacent opposite ends thereof, means of insulating material in said tube and spaced from at least a portion of said tube wall to form an arc passage in air therebetween, said means of linsulating material having a bore therethrough, separate fusible means in said bore and passage, respectively, said fusible means connected between said terminals, current limiting means connected between said fusible means in said passage and one of said terminals, and said between said terminals, and current limit` and narrow as to cause the voltage bore being small to restrict the arc and having a diameter of 1l; inch or less..

6. In a' fuse. a fuse tube of insulating material having terminals adjacent opposite ends thereof, means of insulating material in said tube and spaced from the inner walls thereof to form an annular air space therebetween, means'connected between said terminals including fusible means and resilient means located in said space, said resilient means stressing said fusible means for separating the-terminals of said fusible means upon fusion thereof, said insulating means having an arc restricting bore therethrough, and a second fusible means in said bore and also connected between said terminals.

'I. In a fuse, a fuse tube of insulating material having terminals adjacent opposite ends thereof, means of insulating material in said tube and spaced from the inner walls thereof to form an annular arc chamber therebetween, means connected between said terminals means and resilient means located in said chamber and current limiting means, said resilient means stressing said fusible-means for separat- -mg the terminals of said fusible means' upon including fusible' fusion thereof, said insulating means having an s arc restricting bore therethrough, and a second fusible means in said bore and also connected between said terminals.

8. In a fuse, a fuse tube of insulating material having terminalsadjacent opposite ends thereof, means of insulating material in saidtube and spaced from the inner walls thereof to form an annular arc chamber therebetween, means connected between said terminals including fusible means and resilient means located invsaid chamber, said resilient means stressing said' fusible means for separating the terminals of said fusible means upon fusion thereof, said insulating means heat conducting relation `one end to said resistor tions of said last mentioned fusible means in response to fusion thereof.

9. In a fuse, a fuse tube having terminals adiacent oppomte ends thereof, means -of insulating material in said tube and spaced from the inner walls thereof to form an annular 'arc chamber therebetween. means connected between said terminals including fusible means and resilient means located in said chambei' and current means stressing said fusible means for separating the terminals of said fusible means upon fusion thereof, said current limiting means including a resistor elementpositioned to be in with respect to said fusible means, said insulating means having an arc restricting bore therethrough, and a second fusible means in said bore and also connected between said terminals.

10. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, means of insulating material in said tube and of a size to form an annular arc chamber therebetween, resistor means positioned adjacent one end of said tube 'and connected to one of said terminals, and fusible means limiting means, said resilientl or insulating materna in said chamber and positioned to be heated by said resistor means and connected between said resistor means and the other of said terminals.

11. In a fuse, a fuse tube of a transparent insulating material having terminals adjacent op-l ymaterial in said tubeand of a size to form an annular arc chamber therebetween, resistor means positioned adjacent one end of 'said tube and connected to one of said. terminals, fusible means in said chamber and positioned to be heated by said resistor means and connected at means, and a helical spring in said chamber for biasing said fusible means towards and electrically connecting it to the other of said terminals.

13. In a fuse, a transparent fuse tube of insulating material having terminals adjacent opposite ends thereof, means of insulating material in said tube and spacedfrom the inner walls thereof .to form an annular arc chamber therebetween, means connected between said terminals including fusible means and resilient means located in'said chamber, said resilient means `be ing of helical form to surround said insulating' means and stressing said fusible means for separating'the terminals of said fusible means upon fusion thereof, whereby said helical resilient means provides a readily visible indication of the condition of said fuse.

14. In a current limiting fuse, a length of fusible wire of uniform cross section, solid means of having an arc restricting bore therethrough, a v

second fusible/means in said bore and also con- -nected between said terminals, and a second reallient means for biasing apart the unfused porinsulating material dening a long arc passage for receiving said wire, the cross section area of said passage vconforming to and substantially the same as the cross section of said wire to provide a high arc lvoltage upon fusion of said wire', and current limiting means connected in parallel circuit relation with said length of fuse wire.,

15. Apparatus for limitingheavy overload and short circuit currents comprising current limit.

ing means, means responsive to heavy overload and short circuit currents for automatically establishing an arc in parallel with said current limiting means, solid means oi' insulating material forming an arc passage for said arc to provide an arc voltage at least of a predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of currentiiowing in the circuit, and said arc passage being of such length and restricted cross-section as to cause the arc voltage to rise to said predetermined value in less arc struck by said arcestablishing means to prothana half 'cycle after an arc is struck therein, whereby the current is transferred to said current limitingmeans to limit said current and arc voltage in less than a half cycle. v

16. In a current limiting fuse, a length of fusible wire, solid means of insulating material deilning a long arc passage for receiving said wire,

at least one transverse dimension of said .passage being substantially the same as a transverse dimension of said wire to provide an instantaneous high'arc voltage upon fusion of said wire, and

current limiting means connected in parallel circuit relation with said length of fuse wire.

17. In a current hunting fuse, a length of fusible wire, solid means of insulating material deflning a long. arc passage forvreceiving said wire, the cross-section area of said passage conforming to and being substantially the sameas the cross-section of said wire to provide` a high arc voltage upon fusion of said wire, and current limiting means connected in parallel circuit relation with said length of fuse Qvire.

18.-In a circuit interrupter, arc establishing means, current limiting means `connected in a vide an arc voltage high enough tov transfer all of the current to said current limiting means, and

said means of insulating` material forming a nar? row passage for the arc to restrict the lateral confines. of the arc suiliciently to cause the arc voltage to rise instantaneously to said high value and thereby transfer the current to said current limiting means early enough to'limit the crest of the ilrst half cycle of arcing current.

22. In a circuit interrupter, current limiting means, arc establishing means in 'shunt relation with said current .limiting means, means of insulating material positioned to cooperate with an arc struck by said arc establishing means to provide an arc voltage high enough to transfer all of the current tosaid current limiting means, said means of insulating material forming a narrow passage for the arc to restrict the lateral confines vo'i the arc suiliciently to cause the arc volt-'- age to rise instantaneously to said high value4 and thereby transfer the current to said `current limiting means early enough to limit the crest of the ilrst half cycle of arcing current, and circuit inparallel circuit with said arc establishing means,

means positioned to act on said arc to cause the voltage of said arc to attain at least a predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, and said means acting on the'arc constructed and arranged to cause said arc voltage to rise to said predetermined value at the same instant an arc is struck to cause instantaneous transfer of the current to said current limiting means.

19. In a circuit interrupter, arc establishing means, current limiting means, means positioned to act on said arc to cause the voltage of said arc to attain at least a. predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said means acting on the arc constructed and arranged to cause said arc voltage to rise to said predetermined value at thesame instant an arc is struck and said arc establishing means being associated with said currentlimiting means in such a manner that vsaid instantaneous arc voltage causes instantaneous transfer of the current to said currentlimiting means. v

20. In a circuit' interrupter, fusible means, current limiting means, and means positioned about said fusible means to -act on the varc formed when said fusible means melts to cause the voltage of said `arcl to attain at least a predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of currentk flowing in the circuit, 'said means 'acting on thevarc constructed and arrangedy to cause said arc voltage to rise to said predetermined value at the same instant an arc 4is struck and said fusible means being assovoltage to rise instantaneously to terrupting means in series said current limiting means.

23. In' a circuit interrupter, current limiting circuit relation with means, arc establishing means in shunt relation with said current limiting means, ni'eans of in-` sulating material positioned to cooperate with an arc struck by said arc establishing means to provide an arc voltage'high enough to transfer all of. the current to said 'current limiting means, said means of insulating material forming a narrow passagefor the arc to restrictthe lateral confines of the arc sufficiently to cause the arc said high value and thereby transfer the current to said current limiting means early enough to limit the crest of the ilrst half cycle of arcing current, circuit interrupting means in series circuit relation with said'current limiting means, and said arc establishing and circuitfinterrupting means being automatically operable in response to the passage of currents therethrough above a predetermined magnitude.

24. In a circuit -interruptencurrent limiting means, arc establishing means in shunt relation with said, .current limiting strict the. lateral confines of the arc and is of suil'lcient length to cause the arc voltage to rise instantaneously to said high value and thereby transfer the current to said current limiting means early enough to limit the crest of the first yhalf cycle of arcing current.

25.111 a circuit miei-runter, current iimiung means, arc establishing means in shunt relation with said current limitingmeans, means of insulating material positioned to cooperate with an arc struck by'said arc establishing meansto pro means, means of in sulating material positioned to cooperate with an an arc Struck by said 'means arc establishing means in meansto vide an arc voltage high enough to transfer all of the current to said current limiting means, and said means of insulating material forming a narrow passage for the arc to restrict the lateral confines of the arc sumciently to cause the arc voltage to rise in a small fraction of a half cycle to said high value and thereby transfer the current to said current limiting means early enough to limit the crest of the iirst half cycle of arcing current.

28. In a' circuit interrupter, means, arc establishing means in shunt relation with said current limiting means, means of insulating material positioned to cooperate with arc establishing means to provide an arc voltage high enough to transfer all of the current to said current limiting means, and said means of insulating material forming a narrow passage for the arc to restrict the lateral confines of the arc sufficiently to cause the arc voltage to rise in a few hundred micro-seconds to said high value and thereby transfer the current to said current limiting means early enough to limit the crest of the rst half cycle of arcing current.

27. In a circuit intcrrupter, current limiting shunt relation means of incurrent limiting with said current limiting means,

means, and other fusible means l cause sulating material positioned to cooperate with an arc struck by said arc establishing means to provide an arc voltage high enough to transfer all of the current to said current limiting means, and said means of insulating material forming a narrow passage for the are, said passage having at least one transverse dimension not greater than 11e of an inch to restrict the lateral confines of the arc suiliciently to cause the arc voltage to rise instantaneously to said high value and thereby transfer the current to said current limiting means early enough to limit the crest of the first half cycle of arcing current. l

28. In a circuit interrupter, current limiting means arc establishing means in shunt relation with said current limiting means, means of insulating material positioned to cooperate with an arc struck by said arc establishing means to provide an arc voltage high enough to transfer all of the current to said current limiting means, and

' said means of insulating material forming a bore therethrough the greatest transverse dimension of which does not exceed inch to form a narrow passage for the arc to restrict the lateral confines of the arc sumciently to cause the arc voltage to rise instantaneously to said high value and thereby transfer the current toxsald current limiting means early enough to limit the crest of the first half cycle of arcing current.

29. In a circuit interrupter, means, current limiting means, to act on said arc to cause arc establishing means positioned the voltageof said l arc to attain at least a predetermined value which is greater than the voltage drop through said,

current limiting means for any instantaneous in the circuit. said means acting on the arcconstructed-and arranged to cause said arc voltage to rise t0 said predeterminedvalue atthesameinstantanarc isstruck, saidarcgmeansbeingassociatedwith saidcurrentlimiting meansin suchamannerthat said instantaneous arc voltage causes instantaneous transfer of the current to saidcurrent limiting means, and means responsive to a current limiting operation of said interrupter to insert a gap -in series with said current limiting iiniy intemwt the circuit.

v'Il means,resistaneemeanl.meanl 4said predetermined value 30. In a circuit interrup rent limiting means, and means positioned about said fusible means to act on the arc formed when said fusible means melts to cause the voltage of fusible means, cur` said arc to attain at least a predetermined value.

which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said means acting on the arc 'constructed and arranged to cause said arc voltage to rise to said predetermined value at the same instant an arc is struck, said fusible means being rent limiting means in such a manner that said instantaneous are voltage causes instantaneous transfer of the current to said current limiting connected in series with said current limiting means for interrupting the circuit after current limitation.

, 31. In a circuit interrupter, fusible means, current limiting means,l and means positioned about said fusible means to act"on the arc formed when said fusible means melts to cause the voltage of said arc to attain at least a predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said means acting on the are constructed and arranged to said arc voltage to rise to said predetermined value at the same instant an arc is struck, said fusible means being associated with said current limiting means in such a manner that said instantaneous arc voltage causes instantaneous transfer of the current to said current'limiting means, and other fusible means connected in series with said current limiting means for interrupting the circuit after current limitation, said other fusible means adapted to fuse in response to lower currents than the first-mentioned fusible means. v

32. 'In a circuit interrupter, arc establishing means, current limiting means connected in a parallel circuit with said arc establishing means, means positioned to act on said arc to cause the voltage of said arc to attain at least a .predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said means acting on the -arc constructed and arranged to cause said arc voltage to rise to at the same instant an arc is struck to cause instantaneous transfer of the current to said current limiting means, and means responsive to a current limiting operation of said interrupter to insert a gap in series with said, current limiting means in said parallel circuit, to finally interrupt the circuit.

33. In a circuit interrupter, fusible means, a parallel circuit about said fusible means having current limiting means and other fusible means connected in series, means positioned to act on the are formed upon fusion of said mst-mentioned fusible means to cause the voltage of said arc to attain at least a predetermined value which is greater than the voltage drop through said current limiting means' for any instantaneous value of current flowing in the circuit, said means acting on the arc constructed and arranged to cause said arc voltage to rise to said predetermined value at the same instant an arc is struck to cause instantaneous transfer of the current to said current limiting means, and said other fusible means adapted to finally interrupt the circuit.

34. In a circuit interruptor, arc establishing positioned to act associated with said cur- Assuan Y 7 on lsaid arcl to cause 'the voltage of said arc to 'attmnry at least a predetermined value'which is greater than the'voltage drop through said resistance means 'for any'instantaneous value o1' current flowing in the circuit, said means acting on the arc constructed and arranged to cause said atc 'voltage to rise to said predetermined'value at the same instant an arc is struck. and said arc establishing means being associated with said resistance means in such a manner that said instantaneous arc voltage causes instantaneous I transfer o1' the current to said resistance means.

HRBERT L RAWLINS.