US2044226A - Circuit interrupter - Google Patents

Description

June 16, 1936. H. l.. RAwLxNs CIRCUIT INTERRUPTER Filed Aug. 25, 1953 wenn 1 N A@ gTNESSES:

' ATToR EY Patented June 16, 1936 UNITED STATES CIRCUIT INTERRUPTER Herbert L. Rawlins, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,

Pennsylvania a corporation of Application August 25, 1933, Serial No. 686,760

19 Claims.

My invention relates to circuit interrupters and particularly to high voltage explosion fuses.

One object of my invention is to provide a rellable high voltage expulsion fuse that shall be simple in design, more economical to manufacture, and more satisfactory and reliable in operation than the previously known devices of this type.

Another object of my invention is to provide an improved refill element for use with expulsion fuses, my improved refill element to be inexpensive to manufacture and simple to install.

A further object of my invention is to provide an improved high voltage expulsion fuse which shall include at least two separate arc passages and means for establishing an are in each of the passages, the arc interrupting capacity of the two passages being different in order that the fuse may be equally effective for both high and low values of arc current.

A further object of my invention is to provide an improved circuit interrupter wherein a biased contact member is held against its biasing force by a fusible element which possesses considerable mechanical strength but which is fusible upon the occurrence of relatively moderate overloads to permit the biasing means to cause the opening of the interrupter.

vA further object of my invention is to provide an improved high voltage expulsion fuse which shall utilize a fusible element having sufliciently vlarge physical dimensions to prevent any injury thereto as a result of corona formation, and which shall, at the same time, be operable to effect the opening of the controlled circuit when relatively low magnitude currents flow therethrough.

A further object of my invention is to provide an improved fusible element for use with electrical apparatus. My improved fusible element to have suicient thermal capacity to prevent the operation thereof upon the occurrence of transient overloads of large magnitude and to be operable upon the occurrence of continued overloads of small magnitude.

A further object of my invention is to provide an improved circuit interrupter which shall be operable upon the actuation of thermally responsive means which includes a current carrying heater and means for increasing the normal heating effect of the heater upon the occurrence of predetermined conditions.

A still further object of my invention is to provide an improved expulsion fuse structure which shall include a means for closing one end of the fuse tube and electro-responsive means for opening that end of the fuse tube upon the occurrence of predetermined conditions.

One field for immediate application of my invention is in connection with high voltage potential transformer fuses that utilize boric acid as the source of arc extinguishing gas, and I shall hereinafter describe an embodiment `of my invention as applied to such devices without, however, in any way intending to restrict the scope of my invention except as indicated in the appended claims.

In this type of fuse, a short fusible link is connected to the lower end of a movable rod or plunger, the other end of the rod being affixed to a piston member of conductingl material which is disposed within an insulating tube and is biased upwardly by a coil spring. A flexible conducting shunt disposed Within the coil spring completes the electrical circuit to the stationary contact. Upon the fusing of the link, the rod moves upwardly under the influence of a biasing spring. and establishes the arc within a chamber that is lined with boric acid. The boric acid being decomposed and the resulting outwardly flowing vapor, substantially all of which is superheated steam, extinguishes the arc.

The fuse is restored to an operative condition following each circuit interrupting operation by the removal and replacement of the refill element which includes the boric acid lining for the arc passage, the movable plunger, and the fuse assemblage.- From this, it is immediately apparent that the refill operation consists in the replacing of all of the parts which are subjected to the action of the arc, thereby continuing reliable operation of the device.

The fusible element which is used in this type of circuit interrupter is subjected to very exacting operating requirements. In order to secure satisfactory operation of the fuse, it is necessary that the plunger be moved at a comparatively rapid rate thus necessitating the use of a relatively powerful actuating spring. The entire force of this spring must be opposed by the fusible link itself and at the same time, the link must be capable of fusing when relatively low current flows therethrough. This last requirement is particularly important in circuits such as potential transformer circuits wherein the maximum current carried usually does not exceed one-half ampere. must have considerable mechanical strength, it must be capable of opening the circuit when comparatively low magnitude currents ow therethrough, and at the same time, it must have suiiicient physical dimensions to prevent any injury theretc as a result of corona formation.

Heretofore there has been no satisfactory means for accomplishing these requirements and consequently entirely no satisfactory high voltage fuse has been available for use on circuits having a normal line current of less than amperes. A fuse embodying the features of my invention, however, meets all of these requirements Thus, thpe` fusible link and permits the satisfactory operation of a high voltage fuse upon overload currents as low as one-tenth ampere, this increased range of satisfactory operation being made possible by the novel means which I employ for causing the fusing of the link which holds the movable plunger in the closed circuit position against the spring biasing means.

The features of my invention which I believe to be new are particularly pointed out in the appended claims. For a fuller understanding of those principles and the best mode of applying the same, reference may be had to the accompanying drawing, in which Figure 1 is a side elevational View, partially in section, of an expulsion fuse embodying the principal features of my invention.

Fig. 2 is an enlarged sectional view of a reiiill element for use with the expulsion fuse shown in Fig. 1.

Fig. 3 is a fragmentary sestional view similar to Fig. 2 showing a modified form of refill unit.

Figs. 4 and 5 are end elevations of the reiill unit shown in Fig. 2.

Fig. 6 is an enlarged detailed view of the plunger assemblage shown in Figs. 1 and 2, and

Figs. 7, 8 and 9 are detail views showing the improved heating device utilized in this embodiment of my invention.

The expulsion fuse shown in Fig. 1 includes a cylindrical fibre tube I, having relatively heavy side walls and threaded ends 3 and 5, and two tubular terminal members 1 and 9 of conducting material which have threaded portions II and I3, respectively, for engaging the threaded ends 3 and 5 of the main iibre tube l. The outer surface of each of the terminal members 1 and 9,

which are substantially cylindrical in form, is utilized for engaging suitable contact jaws (not shown). The upper terminal member 1 is provided with a second internally threaded portion I5 for engaging an annular member I1 which is utilized for supporting one end of the operating spring I9. The upper end of the fuse I is closed by means of a cap member 2I having a threaded internal portion 23 which cooperates with a similarly threaded portion 25 on the upper support member 21 for the operating spring I9.

The working parts of the fuse include the main operating spring I9, one end of which engages a threaded portion 29 on the upper support member 21, the flexible conducting shunt 3I disposed within the main operating spring I9 and electrically connected to the upper spring supporting member 21 and the piston member 33 by means of suitable screws 35, and the refill element 31 which engages the piston member 33. The lower end of the operating spring I9 engages a threaded portion 39 on the piston member in substantially the same manner that the upper end engages the support member 21.

The preferred form of the refill element 31 is shown particularly in Fig. 2. It includes a bre tube 4I, having side walls of considerable mechanical strength and a threaded end 42 for engaging the threaded metallic ferrule 44. The fibre tube 4I is lined for the greater part of its length with a cylindrical lining member 43 composed of compressed boric acid. The boric acid lining 43 has a cylindrical passage 45, through the central portion thereof for accommodating the rod or plunger 41, and is further provided with a second passage 49 extending therethrough of considerably smaller cross sectional area than the central passage 45.

, taining rivet 1I.

A threaded fibre plug 5I having an opening 53 therethrough is provided for engaging the upper end of the boric acid lining 43. The lower end of the central passage 45 terminates in a conical throat 55, the lower portion of which is dened by a fibre plug 51, it being desirable to provide material of greater mechanical strength than boric acid for lining those portions of thel arc passage where the thickness of the lining becomes small. The ferrule 44 has a threaded portion 59 for engaging the threaded end 42 of the fibre tube 4I and is provided with an annular shoulder 6I for engaging the end of the fibre plug 51. The central opening 63 through the ferrule 44 forms a continuation of the central passage 45 and the throat 55.

The cylindrical plunger or rod member 41 is preferably constructed of copper; the lower end has a slotted opening 55 therein for engaging one end of the liat fusible strip 61, a soft metal rivet 69 being provided for rigidly ailixing the fusible element 61 thereto. The other end of the fusible link 61 is soldered within a slot 13 in the copper rivet 1I, which is adapted to engage the disk member 15 to hold the plunger 41 against movement under the biasing influence of the spring I9. The disk member in turn abuts against; the annular shoulder 6I in the ferrule 44 of the refill element.

The upper end 11 of the plunger Vrod 41 is threaded for engaging the piston member 33, and is provided with a positioning pin 19 extending therethrough substantially at right angles to the longitudinal axis of the plunger. This pin, as is shown particularly in Figs. 2 and 4, cooperates with two diametrically opposed slots BI in the top portion of the fibre tube 4I of the refill unit in order to prevent rotation of the plunger with respect to the other parts of the refill unit during the refilling operation.

In both forms of refill unit, a wire 83, of somewhat smaller cross sectional area than the cross sectional area of the smaller passage 49 through the boric acid lining 43, is securely afiixed to the upper end of the plunger rod 41 and extends down into the smaller passage 49 where it slidably engages a similar wire 85 extending upwardly into the smaller passage for about one-third of its length. The lower end of the wire 85 is retained in position within a recess 81 in the libre throat member 51.

The retaining disk member 15 which is utilized for holding the plunger member 41 against the biasing force of the operating spring I9 is shown particularly in Figs. 7, 8 and 9. The disk 15 is preferably constructed of a non-metallic resistance material such as carbon or carborundum, and is provided with a central opening 89 to permit the passage therethrough of the shank portion of the rivet 1I, and a pair of annular metal portions 9| and 93 electroplated thereon. The outer plated portion 9| is adapted to engage the annular shoulder 6I on the ferrule 44 in order to provide a good electrical connection between the disk and the ferrule, and the inner plated portion 93 is adapted to engage the plunger re- 'Ihe disk 15 is used for supplying heat to the retaining rivet 1I in order to cause the fusion of the fusible link 61 which is soldered in the slot 13 therein. This arrangement is most suitable for use on very low current circuits, due to the fact that the disk itself possesses considerable inherent resistance to the flow of an electric current; it does permit, however, very accurate calibration of the device.

I prefer to'use one of the lead bismuth alloys, the proportions of which closely approximate those of the eutectic alloy of those metals, for the fusible link 61. These alloys have very sharp melting points, usually in the neighborhood of 80 to 126 C., and permit very close calibration of the thermally responsive element.

In the modification shown in Fig. 3, the resistance disk is parallelled by a second fusible element 95 soldered at one end to the ferrule 44 and at the other to the retaining rivet 1I. This arrangement results in the securing of a parallel path current-carrying heater which is operable upon the occurrence of predetermined conditions to so alter the normal division of current between the two parallel paths that a considerable augmented heating eiect is produced. Such an arrangement is especially suitable for use with higher current circuits wherein the problems of large biasing forces and corona become particularly severe.

The disk 15 is adapted to close the lower end of each type of rell unit, and since the passage 63 through the ierrule 44 is substantially the same diameter as the disk, it offers no impedance to the outwardly flowing arc extinguishingl gas during the operation of the device, the disk being held in position by the same fusible element which causes the operation of the breaker.

The fuse is shown in the closed circuit position in Fig. l, and it will be noted that the main operating spring I9 is tensioned so as to bias the piston member 33 in the direction of the upper terminal member 1. This biasing force is transmitted through the plunger and must be entirely balanced by the fusible element 61. Upon the occurrence of an overload condition in the controlled circuit of sucient magnitude and duration to cause the heat generated in the disk member 15 and transmitted to the fusible element 61 by means of the retaining rivet 1I to effect the fusing of that element, the lower end of the plunger 41 is released and that member is caused to move upwardly into the central arc passage45 under the biasing action of the operating spring I9. An arc is immediately established between the lower end of the plunger 41 and the ferrule 44. This arc will practically instantaneously contact the lower end of the wire 85 thereby putting the conductors 83 and 85 within the smaller arc passage 49 in parallel with the arc. If the current to be interrupted is of small magnitude, the immediate result will be an extinction of the arc in the central passage at the first zero point, all of the current owing through the conductors 83 and 85. Further upward movement of the plunger 41 will then result in a separation of the two wires 83 and 85 which are in slidable conductive relationship, and a second arc will be established within the smaller arc extinguishing passage 49. That passage is particularly adapted for extinguishing small arcs, and the outowing superheated water vapor will cause a rapid cooling and extinguishing of the arc.

If the magnitude of the arc current is large it will cause an immediate fusing of the conducting means (the wires 83 and 85) within the smaller arc passage 49, and the arc will persist in the larger passage 45, although the extinguishing operation is essentially the same. The heat of the arc causes the boric acid lining 43 to evolve superheated steam which flows outwardly longitudinally of the arc through the throat opening 55, the opening 63 in the ferruie, and the continuation of that opening in the lower portion of the terminal member 9 and the hollow cylindrical member 91. The disk member 15 is blown out of the opening through the lower end of the fuse tube immediately upon the generation of any appreciable gas pressure within the device.

The provision of two arc passages and means for establishing an arc in each of those passages is an important feature of my invention in securing satisfactory operation of the device over a Wide range of arc currents. This results from the fact that a suiilcient evolution of arc extinguishing gas from the boric acid lining member of the two arc passages is secured only when the arc is brought into intimate contact with the inner surface of those passages. Thus if a low current arc were drawn into the larger of the arc passages, it would probably exist for an indefinite period of time due to the fact that insuflicient gas would be evolved to eiiect its extinguishment. And while satisfactory interruption of low current arcs is secured within a small diameter arc passage, it is impossible to secure satisfactory interruption of heavy current arcs in such a passage, due to the fact that there is insufficient cross sectional area to permit all of the generated gas to vent without building up pressures within the passage capable of causing severe damage to the entire device.

The operation of Y the modification shown in Fig. 3 is essentially the same as the operation of the structure shown in Fig. 2, except that the first step in the circuit interrupting operation is the fusing of the link 95 which is connected in parallel with the current-carrying heater (the disk 15). The fusion of this link 95 causes substantially all of the current flowing through the interrupter to flow through the heater disk 15. thereby greatly increasing the internal heating produced therein. 'Ihis additional heat is practically immediately transmitted to the fusible element 61 by means of the plunger retaining rivet 1I and causes the fusing of the junction between that member and the fusible element itself, thereby permitting the operating spring I9 to move the plunger to the open circuit position.

Following each circuit interrupting operation of the fuse, it is necessary to restore the device to anoperative condition. 'Ihis is accomplished, in the preferred embodiment of my invention, by the replacing of the refill element 31 therebyrenewing all of the parts of the fuse which come in contact with the arc and which may be damaged thereby. The reilll element 31 is relatively inexpensive, however, due to its simple structure, and while it makes possible the restoration of the fuse to a potential eiectiveness equal to. that when new, the cost of so doing is much less than the cost of restoring any of the previously known high-interrupting-capacity high-voltage fuses to an operative condition.

In the open circuit position, the plunger member 41 has been moved by the operating spring |99. suihcient distance to draw the lower end of the plunger to the top of the central arc extinguishing passage 45. 'Ihe rst step in the insertion of a new refill element consists in the unscrewing of the threaded annular retaining member 91 which engages the threaded portion 96 of the lower terminal member 9. The ilbre tube 4I which forms the body portion of the rell ele- 5 ment 31 and its attached ferrule 44 are then free to drop out leaving only the plunger 41 within the fuse tube I. In order to remove the plunger and re-insert the new rell element, the cap member 2I on the upper terminal 1 is unscrewed, move- 75 ment of the upper support member 21 being prevented by the pin 99 which engages suitable slots (not shown) in the annular member I1. 'I'he upper supporting member 21, the operating spring I9, the piston member 33, and the plunger member 41 are then free to drop out the-lower end of the tube.

The next step is the unscrewing of the plunger member 41 from the piston member 33. Following this, a new refill element 31 is screwed securely intothe piston member 33, the pin 19 preventing rotation of the plunger 41 with respect to the body portion of the refill element. The connected refill element and the plunger mechanism are then inserted in the lower end of the tube I, and the cylindrical retaining member 91 is tightened so as to securely hold the ferrule 44 of the rell element 31 against the cooperating annular shoulder I0l of the lower terminal 9. In order to tension the spring I9, it is necessary to insert a, means for engaging the spring supporting member 21 into the fuse through the opening in the upper annular portion I1, the simplest device for effecting this being a rod having a suitable threaded end for engaging the threaded hole |03 in the top of the supporting member 21. 'I'his rod or other means is screwed into the threaded opening i03 and the spring supporting member 2l is then pulled upwardly. toward the top terminal member ii. The pin 99 is alined with the means which prevents the upper support member 2l from turning with respect to the tube itself, and this means also serves to hold the support member in the upper position while the cap member 2l is screwed on. The upper portion of the fuse tube is thus effectively closed and the entire device has been restored to an operative condition.

Particular attention is directed to the physical dimensions of the fusible element and the heater means therefor. Both are of such size that injurious corona formation will not occur at the voltages of the circuits on which these devices are ordinarily used, and in addition, the heater-fuse combination possesses suflicient thermal capacity to permit the device to carry heavy overload currents for short periods without in any way decreasing the ability of the device to function upon the occurrence of prolonged low current overloads.

It will thus be seen that I have disclosed an improved high voltage expulsion fuse which is particularly suitable for use on very high voltage circuits through which low magnitude currents normally flow.

In addition, it will be seen that I have disclosed an improved refill element for use with expulsion fuses which permits the replacement, at a very moderate cost, of all of the parts of the fuse which are exposed to the action of the arc. Further, I have disclosed means whereby a fusible element possessing considerable mechanical strength and suiiicient large physical dimensions to prevent any injury thereto as a result of corona formations may be utilized on very low current circuits.

Besides these features capable of wide adaptation to the expulsion fuse art, I have disclosed certain specific forms of construction which are particularly effective in carrying out the general objects of my invention. One of these forms is an improved heater means for the fusible element of a circuit interrupter which utilizes a current carrying element of non-metallic resisting material and conducting means in intimate contact therewith for transmitting the heat generated to the fusible element.

Another of these improved forms is a heater for a thermally responsive fusible element which utilizes a current carrying electro-responsi"e device in parallel with the heater for increasing the normal heating effect thereof upon the occurrence of predetermined conditions.

While, in accordance with the patent statutes, I have given the foregoing details of a preferred practical embodiment of my invention, it is to be understood that many variations from the precise form described are possible and may for some applications be desirable. I desire, therefore, that the language of the accompanying claims shall be accorded the broadest reasonable construction and that my invention be limited only by what is explicitly stated in the claims and by the prior art.

I claim as my invention:

l. In a circuit interrupter, means for defining the walls of an arc chamber, a rigid plunger means movable within said arc chamber to a closed circuit position and to an open circuit position, means biasing said plunger means toward the open circuit position, thermally responsive means for restraining said plunger means in the closed circuit position, against said biasing means, and means for heating said thermally responsive means comprising a current carrying heater and an electro-responsive means for limiting the current in said heater except upon the occurrence of predetermined electrical conditions.

2. In a circuit interrupter, means for defining the walls of an arc chamber, conducting means movable within said arc chamber to a closed circuit position and to an open circuit position, spring means biasing said movable means toward the open circuit position, thermally responsive means for restraining said movable means in the closed circuit position against said biasing means, and heater means for causing said thermally responsive means to release said movable means, said heater means comprising a currentcarrying heater unit and a current-carrying electro-responsive unit, normally connected in parallel with said heater unit, for limiting the current flow in said heater unit until the occurrence of predetermined electrical conditions.

3. In a circuit interrupter, means for defining v the walls of two connecting chambers, means movable Within one of said chambers to a closed circuit position and to an open circuit position, spring means disposed within the other of said chambers for biasing said movable means toward the open circuit position, fusible thermally responsive means for restraining said movable means in the closed circuit position against said biasing means, and heater means for causing the release of said movable means, said heater means comprising a current-carrying heater unit, and a current-carrying fusible element, normally connected in parallel with saidheater unit, for limiting the current iiow in said heater unit until the occurrence of predetermined electrical conditions.

4. In a circuit interrupter, tubular means for defining the walls of an arc chamber, a rigid plunger means movable Within said arc chamber to a closed circuit position and to an open circuit position, means biasing said plunger means toward the open circuit position, fusible thermally responsive means disposed within said arc chamber for restraining said phmger means in the closed circuit position against said biasing means, and means for heating said fusible means comprising a current-carrying heater unit and a current-carrying electro-responsive unit connected in -parallel with said heater means, said electro-responsive unit operating upon the occurrence of predetermined conditions to cause an increase in the normal heating effect of said heater unit.

5. In an electro-responsive device, a fusible element and a heater means therefor comprising a current carrying body of non-metallic resistance material, means extending through said body for conducting the heat generated therein to said fusible means, and a current-carrying electroresponsive means connected in parallel with said current-carrying body of resistance material, said electro-responsive means acting upon the occurrence of predetermined conditions to so change the normal division cf current iiow between said parallel paths so that a substantially greater than normal proportion of the current ows through said resistance unit.

6. In an electro-responsive device, a fusible element, and a heater means therefor comprising a current-carrying body of non-metallic resistance material, means vextending through said body for conducting the heat generated therein to said fusible means, and a current-carrying fusible means connected in parallel with said current-calrying body of resistance material, said means being fusible upon the occurrence of predetermined conditions to cause substantially all of the current flowing through said device to iiow through said body of resistance material.

'7. In a circuit interrupter, tubular means at least partially of insulating material, a cap means of conducting material for closing one end of said tubular means, a means of conducting material supported at the other end of said tubular means in such manner that at least a portion of the central passage through said tubular means will be open, means supported on said cap means and movable within said tube to open the circuit, means biasing said movable means to the open circuit position, and means for retaining said movable means in the closed circuit position against said biasing means, said retaining means comprising a fusible means, and a member of non-metallic resistance material which is adapted to be held against said tube and said conducting means by said biasing means in such manner that said tube is releasably closed when said interrupter is in the closed circuit position.

8. In a circuit interrupter; tubular means, at least partially of insulating rmaterial; conducting means supported adjacent one end df said tubular means; fusible means within said tubular means; and means for ,substantially closing one end of said tubular means and for electrically connecting said fusible means with said conducting means, said means comprising a heater means for causing the fusion of said fusible mea-ns upon the occurrence of predetermined conditions, and having proper dimensions for closing one end of said tubular means; said connecting means being normally retained in position by, said fusible means but being movable upon the fusion of that means to open one end of said tubular means.

9. In a circuit interrupter; tubular means for defining an arc passage, at least a portion of which is lined With a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc; conducting means movable through said arc passage to establish an arc therein; fusible means for controlling the operation of said arc drawing means; and heater means for causing the fusion of said fusible means upon the occurrence of predetermined conditions, said heater means being normally adapted to close one end of said arc passage and being movable, during the circuit interrupting operation, to open at least a portion of one end of said arc passage in order to permit the venting of the gas evolved from said lining.

l0. In a circuit interrupter; tubular means for defining an arc passage, at least a portion of which is lined with a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc; conducting means movable through said arc passage to establish an arc therein; fusible means for controlling the operation of said arc drawing means; and heater means for Causing the fusion of said fusible means upon the occurrence of predetermined conditions, said heater means comprising a member of nonmetallic, resistance material which is so proportioned that it normally closes one end of said arc passage and which is movable, during the circuit interrupting operation, to open one end of said arc passage in order to permit the venting of the l gas evolved from said lining.

1l. In a circuit interrupter; tubular means for defining an arc passage, at least a portion of which is lined with a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc; means for closing one end of said tubular means; spring biased, conducting means movable through said arc passage to establish an arc therein; fusible means for preventing movement of said arc drawing means except upon the occurrence of predetermined conditions; and a current-carrying heater means, lthermally conductively disposed with regard to said fusible means, for causing the fu.'- sion thereof upon the occurrence of predetermined conditions; said heater means being so proportioned that it normally closes one end of said arc passage, being held in that position by said spring biased, arc drawing means, and being movable, during the circuit interrupting operation, to open one end of said passage in order to permit the venting of the gas evolved from said lining.

12. In an expulsion circuit interrupter;` tubular means for defining an arc passage, at least a portion of which is lined with a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc; means for closing one end of said arc passage, the other end of said arc passage being open during the circuit interrupting operation; a spring biased, plunger means movable through said arc passage to establish an arc therein; fusible means for normally restraining said arc drawing means in the closed circuit position; and current-carrying heater means for causing the fusion of said fusible means upon the occurrence of predetermined conditions; said heater means comprising a substantially non-inductive resistance element, being 'so proportioned that it substantially closes said other end of said arc passage, except during the circuit interrupting operation, being held in that position by the reaction forces exerted by said spring biased plunger, and being adapted to be moved in the opposite direction to that in which said arc drawing plunger is moved, during the circuit interrupting operation, by the gas evolved from said lining; said movement of said heater means causing said other end of said arc passage to be opened so as to permit substantially free venting of said gas.

13. In a circuit interruptor; tubular means for denning an arc passage; means for closing one end of said arc passage; a conducting seat positioned at the other end of said passage; means, including a spring biased fusible element, for drawing an arc within said arc passage during the circuit interrupting operation; and a substantially non-inductive, current-carrying, heater means for causing the fusion of said fusible element upon the occurrence of predetermined conditions, said heater means including a member of non-metallic resistance material which is held against said seat by the reaction forces of said spring biased arc drawing means.

14. In a circuit interrupter; tubular means for defining an arc passage; means for closing one end of said arc passage; a conducting seat positioned at the other end of said passage; means, including a spring biased fusible element, for drawing an arc within said arc passage during the circuit interrupting operation; and a substantially non-inductive, current-carrying, heater means for causing the fusion of said fusible element upon the occurrence of predetermined conditions, said heater means including a member of non-metallic, resistance material, having a passageway therein, which is adapted to be held again said seat by the reaction forces of said spring biased arc drawing means, said reaction forces being transmitted to said resistance member through the agency of a conducting means, having an enlarged head portion, which means extends through said passageway and serves to conduct the heat generated within said resistance element to said fusible arc drawing means.

i5. In a circuit interrupter, conducting means movable from a closed circuit position to an open circuit position to open the electrical circuit through said interrupter, means biasing said movable means to the open circuit position, and electro-responsive means for normally holding said movable means in the closed circuit position against said biasing means, said holding means including a fusible element, heater means for said fusible element comprising a hollL-w member of resistance material, and a means of conducting material which extends through said hollow heater member for mechanically 'and thermally connectingv said fusible element and said heater, said means of conducting material having an enlarged head portion for engaging said heater, and both said fusible element and said heater being subjected to substantially all the force of said biasing means.

16. In a. circuit interrupter, conducting means movable from a closed circuit position to an open circuit position to open the electrical circuit through said interrupter, tension spring means biasing said movable means to the open circuit position, and electro-responsive means for normally holding said movable means in the closed circuit position against said biasing means, said holding means including a fusible element, -heater means for said fusible element comprising a hollow member of non-metallic resistance-material, means for supporting said heater member, and a rod-like member of conducting material which extends through said hollow heater member for mechanically and thermally connecting said fusible element and said heater, said rod-like member having an enlarged head portion for engaging said heater, and both said fusible element and said heater being subjected to substantially all the force and of said biasing means.

17. In a circuit interrupter, tubular means for defining an arc passage, a seat positioned at one end of said tubular means, means movable from a closed circuit position to an open circuit position to open the electrical circuit through said interrupter and establish the arc incident thereto within said arc passage, means biasing said movable means to the open circuit position, electro-responsive means including a fusible element for normally holding said movable means in the closed circuit position against said biasing means, and a heater means for causing the fusion of said fusible element upon the occurrence of predetermined conditions, said heater means including a member of resistance material which is held against said seat by the reaction forces of said biasing means.

18. In a circuit interrupter, tubular means for defining an arc passage, a conducting seat positioned at one end of said tubular means, means movable from a closed circuit position to an open circuit position to open the electrical circuit through said interrupter and establish the arc incident thereto within said arc passage, means biasing said movable means to the open circuit position, and electro-responsive means for normally holding said movable means in the closed 'circuit position against said biasing means, said holding means including fusible element, heater means for said fusible element comprising a hollow member o resistance material, and a means of conducting material which extends through said hollow heater means for mechanically and thermally connecting said fusible element and said heater, said heater means being adapted to engage said seat and being normally held against said seat by the reaction force of said biasing means which force is transmitted thereto by said means of conducting material.

19. In a circuit interrupter, tubular means for defining an arc passage, a conducting seat positioned at one end of said tubular means, conducting means movable from a closed circuit position to an open circuit position to open the electrical circuit through said interruptor to establish the arc incident thereto within said arc passage, resilient means biasing said movable conducting means to the open circuit position, and electro-responsive means for normally holding said conducting means in the closed circuit position against said biasing means, said electroresponsive means including a fusible element, heater means for said fusible element comprising a`hollow member of non-metallic resistance material, and a means of conducting material having a body portion which extends through said hollow heater means for mechanically and thermally connecting said heater and said fusible element, at least the edge portions of said heater member engaging said conducting seat, said means of conducting material having an enlarged head portion for engaging said heater adjacent the central opening therethrough, and said heater being held in engagement with said conducting seat by the reaction force of said resilient biasing means which force is transmitted thereto by said means ofv conducting material.

HERBERT L. RAWLINS.

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