US2389392A - Circuit interrupter - Google Patents

Description

Nov. 20, 1945. A. P. sTRoM 2,389,392

CIRCUIT INTERRUPTER Filed July 7, 1944 uff/M l Patented Nov. 20, 1945 UNITED STATES PATENT oEEicE CIRCUIT INTERRUPTER j Albert P. Strom, Forest Hills, Pa., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Applicaugn July 7, m44, serial No. 543,815 1o claims. (ci. 20o-12o) This invention relates to circuit interrupters and, more particularly, to circuit in-terrupters wherein the establishment of an arc results in the evolving of an arc extinguishing gas from vcertain portions of the circuit interrupter whereby the arc is ultimately extinguished.

Efficient extinction of an electrical arc may be secured by applying adjacent to the arc a, material which on being subjected to the heat of the arc will evolve an unionized cooling gas which will extinguish the arc and render the restriking of the arc impossible. A good material for the purpose should be electrically insulated at all times. It has been found that substances giving of! water and nitrogenous gases are particularly satisfactory materials for employment in circuit breakers for this purpose. According to'the invention it has been found that compounds of ammonia and boric acid are exceptionally ecient arc extinguishing materials.

The object of this invention is to provide for applying in circuit interrupting devices com pounds capable of evolving nitrogeneous gases and water vapor as arc extinguishing gases when subjected to an electrical arc.

A further object of the invention is to provide for molding compounds lof ammonium and boric oxides into solid members suitable for use in circuit interrupters as arc extinguishing and confining members.

Other objects of the 'invention will in part; be obvious and will in part appear hereinafter.

For a fuller understanding of the objects and advantages of the invention, reference should be had to the following detailed drawing of the invention, in which:

`Figure 1 is a cross section through one form of circuit interrupter,

Fig. 2 is a cross section through an elevation of a fuse link,

Fig. 3 is a cross section through an elevation of a modified form of fuse link,

Fig. i` is a cross section along line IV-IV of Fig. 3,

Fig. 5 is a view in elevation of another form of circuit breaker, and

Fig. 6 is a partial section along line VI--VI of Fig. 5.

Referring to Fig. 1 of the drawing, there is illustrated a circuit interrupter comprising one contact member I0 in the form of a ferrule and having an aperture I2. The contact member I 0 is threadedly engaged with a tube or sleeve I4 composed of a material which is insulating and capable of evolving an arc-extinguishing gas in the 55 presence of an electrical arc. A second relatively movable contact member I6 is disposed for reciprocating motion within a passage I8 within the member I4. The contact member I6 may be reciprocated downwardly until it is in physical contact with the contact member I0 whereby a circuit may be closed. Upon moving the contact member I6 upwardly, a circuit so established will generally form an arc between Ithe two members I0 and I6. The arc so established will cause decomposition of the member I4 due to i-ts heat and an arc-extinguishing gas will be evolved. 'Ihe arc-extinguishing gas resulting will flow to the aperture I2 and will exert a cooling and deionizing eiect which will extinguish the arc.

According to the present invention the member I4 is composed of a. compound of ammonia and boric Voxide capable of evolving large amounts of arc extinguishing gases on being subjected to arcing conditions. A particularly satisfactory compound for the use of this invention is ammonium pentaborate having the formula The Water of hydration may vary from 5H2O to 8H2O. Another applicable ammonium' pentaborate compound with more water of hydration per unit weight has the following formula: NH4.BsOa.4HzO.Ammonium tetraborate (NH4) 2.B401.4Ha0

and ammonium acid tetraborate NH4.HB4O1.3H2O are related compounds which may be used in circuit interrupters as gas evolving members. Ammonium pentaborate is particularly effective since it evolves large quantities of nitrogenous gases such as ammonia and nitrogen and large quantities of water when subjected to the heat of an arc. The ammonium pentaborates have been employed with highly satisfactory 'results in circuit interrupters.

In order to make members such as I4 in Fig. 1 of the drawing it has been discovered that the ammonium pentaborate can be pressed readily when it has been wet with water whereas in a dry condition it is difficult to mold. Powdered ammonium pentaborate wetted with water is put into a steel mold having a cavity corresponding to the shape of member I4 and when pressed at a pressure of several hundred pounds per square inch a hard solid block is produced. The block is put in an oven and when dry is mechanically strong and is capable of withstanding :the conditions'present in circuit interrupters. The

32, extends to a dry cylinder of ammonium pentaborate has excellent high temperature electrical resistance.

The ammonium borate compound may be combined with other materials to provide for predetermined characteristics. For example, the ammonium borate may be admixed with a resinous binder, which may be either a thermoplastic or a thermosetting resin, and when molded under heat and pressure a hard block of material is thereby produced. Thus ,a/ mixture of from 50 to .95 parts of ammonium pentaborate with from 50 to 5 parts of a resin such, for example, as a vinyl monomer, such as monostyrene, with a catalyst, urea resin or a. melamine resin may be formed into a solid member under heat and pressure. Other binders may be employed to provide for predetermined characteristics. In making resin bonded members it may be desirable to incorporate a small portion of fibrous materialto provide for predetermined strength characteristics. For example, 100 parts of ammonium pentaborate is mixed with 3 parts of cotton flock and then '70 parts of a res- V inous binder dissolved in a solvent is added. On

thorough mixing a stiff dough-like mass will be produced. The mass may be put into molds and when subjected to heat and pressure a solidly bonded member is attained. The resinous binder, if employed in progressively large proportions, imparts progressively greater mechanical strength and greater moisture resistance. Thus a memgreat number of times with successful extinction of the arc.

Referring to Fig. 2 of the drawing there is illustrated a fuse consisting of a tube 20 prepared from a molded ammonium borate composition as described herein. The tube y20 is threadedly engaged with a metallic ferrule 22. A removable fuse link unit 23 is adapted to be removably secured within the tube 20 by clamping the terminal head portion 24 thereof between the outer end of the ferrule 22 andan end cap 26 threadedly engaged therewith. The fuse link unit 23 within the tube 20 includes an upper terminal portion 28 connected by a fusible and strain means 30 to a lower terminal strip 32, all disposed within a relatively small arc confining and extinguishing tube 34. The tube 34 is preferably composed of the composition of this invention carrying a higher proportion of ammonium pentoborate than the tube 20. 'I'he lower terminal strip 32 is resiliently urged away from the upper terminal strip 28 by a spring 36 held in compression vbetween the tube .34 and a pin 38 in the lower end of the strip.. A flexible conductor tail 46 connected by soldering lor the like to'terminal iower ,ferrule 42 and is connected thereto by the thumb screw 44 to maintain an electrical contact.

'I'he main function of the smaller tube 34 is to confine low current arcsresulting from the fusion of the means 30 so that the gas evolving composition comprising the tube is in close proximity to the link/ and thereby assures a rapid and eilicient extinction of arcs of low current.

When a relatively high current, such for example as a short circuit, fuses the means 30, the small tube 34 is sufficiently weak to burst, thereby relieving the gas pressure developed and permitting the arc-extinguishing gases to expand withinA the larger volume within tube 20 which, when subjected to the arc, develops su'iicient gas to assure the extinction of the arc. For these reasons, the tube 20 is preferably composed or prepared from a composition having greater strength which may be attained by employing therein more resinous binder than present in the inner tube 34.

Referring to Fig. 3 of the drawing there is illustrated a modified form of fuse known as a refill element type for use in a fuse assembly as shown in H. L. Rawlins Patent 1,976,634, issued October 9, 1934. The fuse illustrated comprises a cylindrical member 50 which may be molded from the wetted ammonium pentaborate or the ammonium pentaborate combined with a resinous binder or a fibrous resin similar as described herein. The cylindrical member 50 is provided with a main bore 52 and a smaller bore 54 either by molding or machining. Within the smaller portion 54 is disposed a cylindrical tube 56 composed of the ammonium pentoborate preferably alone since strength is not critical within this smaller tubing. An arcing rod 58 positioned within the larger bore 52 is connected by a fusible and strain means 60 to a lower terminal ferrule 62, a shunt between the arcing rod 58 and the ferrule 62 is provided by the overlapping of the wires 64 and 66 connected, respectively, to the arcing rod 58 and the terminal ferrule 62.

The construction of Fig. 3 enables the efficient extinction of arcs of different current strength. When the fusible means 60 blows on a relatively low current, a spring or other biasing means (not shown) is employed to move the arcing'rod 58 upward in the bore 52 whereby to elongate the.

arc. With a low current arc, the overload is, transferred to the smallwire 64-66 within the tube 56. 'Continued movement of the arcing rod 58 will result in an eventual separation of the wires` 64 and 66 with the eventual development of an arc within the smaller tube 56. Due to the heat of the arc, an `arc-extinguishing gas will be evolved from tube 56 which will extinguish the arc within the small bore.

When the fuse means 60 fuses on high currents, the relatively small wires 64 and 66 will also fuse and the arc developed there will be transferred to the large bore 52. Therefore, an arc will be drawn between the lowerend of the rod 53 and the ferrule 62. The high current arc so drawn out will cause the decomposition of the walls of bore 52 of the member 56 and thereby will cause the generation of a suflicient amount of gases to cool and deionize the large current arc.

A particularly desirable application for the moldable composition of the present invention is for use in connection with the disconnecting switch 10 illustrated in Figs. 5 and 6. The switch is shown and described in greater detail in the patent to H. L.'Rawlins No. 2,308,026, issued January 12, 1943.

The switch 10 is mounted on spaced insulating supports 12 and 14 composed of porcelain or the like. The lower insulating support 12 carries a cap 16 bearing a lower terminal portion 18 for connection to alignment conductor. The cap 16 is provided with a hinged tongue upon which is mounted a split blade switch structure 82 movable about hinge bolt 84. A cap 85is carried by the upper insulating support 14, the cap being provided with an upper terminal portion 86 for connection to a second line conductor to be put in circuit with the line conductorVV connected to 18. A break tongue 99 provided on the cap 85 is adapted to engage the split blades 82 to complete the circuit. An apertured lug 92 at the upper end of the structure 82 is provided for receiving a hook stick operating member or the like.

A bracket 96 pivotally mounted on pin 98 on the switch blade structure 82 supports an offset auxiliary switch blade 94. The auxiliary switch blade 94 is resiliently urged for counterclockwise movement about pivot 98 by the spring 91. The auxiliary switch blade 94 is adapted to engage the spring biased contact member 99 mounted on an arm 88 fastened to the cap 85, as shown in Fig. 6 of the drawing.

An arc confining and extinguishing structure comprising a pair of laterally extending plates fastened to arm 88 and provided with a liner |02 is disposed about the contacting members 94 and 99. The liners |92 ma'y be formed of ammonium borate compound alone but preferably comprises a. resinous mixture embodying the ammonium pentaborate. The liners |02 composed of a resinous composition embodying ammonium pentaborate may be drilled to provide holes for the machine screws |84 for maintaining the arc extinguishing composition in place.

When a hook stick is applied to the lug 92 and the switch blades are pulled vcounterclockwise in Fig. 5 of the drawing about pivot 84, the blades 82 will separate from the break contact 90, but the auxiliary switch blade 94 will remain in electrical contact with the resilient contacts 99 and will carry the current. The resiliency of the contacts 99 is such as to retain the switch blade 94 against the force of spring 91, but if the counterclockwise motion be continued, eventually the blade 94 will be forcibly drawn through the spring contacts 99 and an extremely rapid separation of the switch blade 94 and contacts 99 will take place. During separation an arc will be drawn between switch blade 94 and contacts 99. The plates |82 of the gas-evolving composition when subjected to such an arc will develop a large quantity of unionized arc-cooling gases composed mainly of water vapor. This will assure a rapid and effective extinction of the arc.

The composition of the invention is satisfactory for the fabrication of liners, arc chutes, and other insulating and gas-evolving members for use in all types of circuit breakers. The circuit interrupters illustrated in the drawing are not intended to be limiting but are exemplary of the use of the ammonium borate materials.

While the molding of moldable mixtures embodying the ammonium borates have been described in some detail, it will be appreciated that tubes such as 29 and 84 of Fig. 2 may be prepared by other means. For example, sheets of paper carrying some binder and to which a quantity of powdered ammonium borate has been deposited can be molded into tubular structures and when pressed and dried a solid tube member is thereby produced. Other methods of providing structures of predetermined shape will be obvious to those skilled in the art and need not be detailed herein further. i

Having described preferred embodiments of my invention, I wish it to be understood that the invention is not limited to the particular embodiments disclosed herein since it is apparent that many changes and modifications may be made in the several compositions and the various structures shown `without departing from the broad spirit and scope of the invention.

I claim as my invention:

l. In an electric circuit interrupter, conductor means between which an arc is formed on interruption of the electric circuit, arc confining and extinguishing means so disposed with respect to l the conductor means as to provide for evolution of an arc extinguishing medium when subjected Vto an arc, the arc connng and extinguishing means comprising an ammonium borate compound. g

2. In an electric circuit interrupter, conductor means between which an arc is formed on interruption of the electric circuit, arc confining and extinguishing means so disposed with respect to the conductor means as to provide for evolution of an arc extinguishing medium when subjected to an arc, the arc confining and extinguishing means comprising an ammonium pentaborate.

3. Ina'n electric circuit interrupter, conductor n means between which an arc is formed on interruption of the electric circuit, arc confining and extinguishing means so' disposed with respect to the conductor means as to provide for evolution of an arc extinguishing medium when subjected to an arc, the arc connning and extinguishing means comprising a solid body of4 ammonium borate.

4. An arc confining and extinguishing structure comprising an ammonium berate.

5.4 An arc confining and extinguishing structure comprising ammonium pentaborate.

l6. An arc confining and extinguishing structure comprising an ammonium borate and a binder.

7. An arc confining and extinguishing structure comprising an ammonium borate and a nitrogenous binder.

8. An arc confining and extinguishing structure comprising ammonium pentaborate and a resinous binder.

9. In a fuse, a fuse tube, conducting means in the fuse tube between which an arc is formed on interruption of the circuit, the fuse tube composed of sheets of fibrous material. a binder and ammonium borate, the ammonium borate evolving an arc extinguishing gas when subjected t0 the action of an arc.

10. An are coniining and extinguishing structure composed of sheets of nbrous material and ammonium borate applied to the sheets.

ALBERT P. STROM.

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