US2644048A

US2644048A - Circuit interrupter

Info

Publication number: US2644048A
Application number: US175332A
Authority: US
Inventors: Russell E Frink; Eugene H Fischer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-07-22
Filing date: 1950-07-22
Publication date: 1953-06-30
Anticipated expiration: 1970-06-30
Also published as: FR1046704A

Description

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` WITNESSES:

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CIRCUIT INTERRUPTER Filed July 22, 1950 5 Sheets-Sheet 3 INVENTORS Russell E.Frink and Eugene H.Fischer.

ATTORN Patented `lune 30, 1953 UNITED STATES PATENT OFFICE CIRCUIT NTERRUPTER Application `luly 22, 1950, Serial No. 175,332

(Cl. G-144) 14 claims. 1

This invention relates to circuit interrupters in general, and more particularly to arc extinguisheing structures therefor.

A general object oi our invention is to provide an improved arc extinguishing structure which will more erlectively interrupt the circuit therethrough than has been attained heretofore.

e. more speciiic object is to provide lan im proved spaced plate type oi arc extinguishn structure for circuit interrupters or" the air brea.; type, in which improved plate coniiguration utilized to more readily assist arc extinction at an early current zero.

A further object is to provide an improved plate material for circuit interrupters oi the ioregoi type which will have improved electrical chanl acteristics at relatively high temperatures.

A more specic object is to provide an improved refractory 'type spaced plate arc extinguislfier ol" the type utilizing slotted plates in which longitudinally extending grooves, substantially paralm lel to the direction of the slots, are utilized to prevent reignition of the extinguished arc after a current zero.

Another object is to provide an improved chute in which the arc is made to assume a serpentine or sinuous path as it moves outwardly through the chute in which longitudinally extend-s ing grooves are provided to form a lengthened creepage path in parallel with the arc to prevent reignition of the extinguished varc alter a current Zero.

It is still a further object of our invention to provide an improved refractory material for use in an arc chute against which the arc is moved, the improved electrical characteristics of which will more quickly bring about arc extinction.

A further more speciiic object is to provide a slotted spaced plate type of are extinguisher in which the plates are formed of a material having" improved electrical characteristics.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawn ings, in which Figure l is a side elevational view, partially in vertical section, ci a circuit interruptor embodyw tact it.

Fig. 5 is a vertical sectional view taken along the line V-V of Fig. 4 showing only the arc chute sub-assembly, and

Fig. 6 is an enlarged plan view in section tal-:en along the line VI-VI of Fig. 5 through one of the fins or projections extending outwardly from one wall of the arc chute of Fig.

Referring to the drawings, and more particularly to Fig. 1 thereof, the reference numeral i designates a circuit interruptor of the air break type mounted upon a suitable panel structure 2. Briefly, the circuit interruptor l comprises a blowout coil il, a U-shaped magnetic circuit il; Contact structure t separable to establish an arc and an arc extinguishing structure for quickly elicot-n ing the interruption of the established arc.

The contact structure 5 comprises a'terrninal stud l' surrounded by a bushing il of a suitable insulating material. The terminal stud s supports a stationary contact plate il, the latter in turn supporting a main contact lll, a secondary contact il and a relatively stationary arcing contact it. Another terminal stud, not shown, has pivotally mounted thereon a movable Contact arm i3 carry ing a movable bridging contact it, a movable secondary Contact l5 and a movable arcing con-= Also electrically connected to this second terminal stud, not shown, is a main contact il'.

During the opening operation, pivotal clockwise opening rotative motion of the Contact arm i3 takes place caused by the actuation of a suitable mechanism, which forms no part of our invention. The bridging contact it rst separates from the stationary main contacts it, il to force the series current to pass through the secondary and arcing contacts il, lli and it, i5. Continued opening rotative motion of the contact arm it subsequently causes separation between the secondary contacts il, i5 to force the current to pass through the arcing contacts Further opening rotative motion of the pivotally mounted movable contact arm I3 causes separation between the arcing contacts l2, I6 to establish an arc therebetween. Because of the loop circuit formed by the two terminal studs, and because of venting provided through the vent 23, the arc, established between the separated arcing contacts I2, I6, will bow upwardly to conu tact the arc horn lll in the manner indicated by the broken line I9. The attachment of the lefthand arc terminal to the arcing plate or horn lll will insert into series circuit the blowout coil 2li which-will, upon being energized, magnetize the U-shaped magnetic structure 4 to thereby set up a transverse magnetic field 2i between the pole plates 22, as shown in Fig. 2. This magnetic movable contact arm I3 to the other terminal stud for the interrupter, not shown.

As mentioned, the 'transverse magnetic field 2l, set up between the pole plates 22 by the blow out coil 26, forces the arc 2E upwardly into the arc chute 6 which comprises a plurality of refractory spaced plates 21, which do not evolve gas upon contact with the established arc. It will be observed that each plate 21 has a tapered slot 28 extending inwardly from the lower side 29 thereof with the upper end 30 of the slot 2i! e slightly off center. That is, the center line 3i of the plate 21 passes slightly to the right of the upper end 30 or the slot 29 of the plate 21 shown in Fig. 2. llhe immediately adjacent plate 21 of Fig. 2, has its slot 28 turned 180 to that oi the slot 28 of the first plate 21 in Fig. 2, so that the second plate 21 has the upper end 3c of its slot 28 disposed to the right of the center line 3i of Fig. 2. The net result is, therefore, that the upper ends 3U of the several slots 2t are staggered *L about the center line 3l, so that when the arc 28 is at the upper ends of the slots 28 it is forced to assume a zig-zag configuration, as more clearly shown in Fig. 3.

For the theory pertaining to the manner oi' arc interruption in a spaced refractory plate type of arc extinguisher, reference may be had to United States Patent 2,442,199, issued. May 25, 1948 to Robert C. Dickinson and Russell E. lhinli, and assigned to the assignee of the instant applica1 tion. This Patent 2,442,199 sets forth in detail the theory of arc extinction which is assumed to take place, and also mentions vprior patents which forni a background for this type of arc interrupu tion.

It will be, observed that each of the plates 21 has provided therein a plurality of srnall slots or grooves 32 in the surface plane of the plate, on each side thereof, which extend substantially parallel to the direction of the narrow tapered portion 39 of the slot 28, the purpose for which will be more fully described hereinafter. 1t will also be observed that spacers 34, preferably formed of asbestos rope and cemented to the reM fractory plates 21, are utilized to space the plates 21 the desired distance apart. The plates 21 and the spacers 34 are cemented together, as menn tioned, and together with the arcing horns I8, 24 form a sub-assembly 35, which is placed downwardly within the rectangular arc chute housing 35, the latter being disposed between the pole plates 22 of the blowout structure 4. After the sub-assembly 35 has been placed within the arc chute jacket 36, a pair of insulating holding strips 31 are utilized to prevent the gas pressure from forcing the sub-assembly 35 upwardly out of the are chute jacket 36. Preferably, bolts 3S are employed to secure the holding strips 31 to the upper edges of the arc chute jacket 3G.

The slots 28 may extend in some instances for a distance of 7 to 9 inches from the lower ends 28 of the plates 21. As mentioned, the upper ends 3|) of the slots 28 are alternately offset so that when the arc 26 is driven up into these ,notches or slots 28, it is lengthened, restricted accalmie in cross-section and subjected to the intense dei ionizing action of a powerful, magnetically-in duced gas blast. All of these factors directly oi' indirectly bring about deionization of the arc path, and the arc is compelled to continuously ionize fresh quantities of gas. If at the time interval in the region of current zero, the rate of de-ionization exceeds that at which the arc can produce ionization, and all insulation paths parallel to the arc are able to withstand transient and normal restored Voltage, interruption of the arc 26 results.

When an interruption takes place, the gas path which immediately before had been a conductor, does not instantly become a good insulator. At the .instant immediately following current zero, the restored voltage transient begins to be impressed across the space previously occupied by the arc, and current starts to flow in the reverse direction. The product of this current and the voltage across the arc chute represents energy which is re-ionizing the gas and further heating the solid insulation. If the rate of deionization of the gas path and the rate of conduction of heat away from the surface of the solid insulation is greater than the rate at which the arc is ionizing and heating, then the current will be interrupted. We have found that on many successive interruptions, this leakage current flowed from 0.1 to 0.25 cycle after the point of apparent interruption, and that its current magnitude was greater than 0.1 ampere.

We have also discovered that the limit of interrupting ability of the circuit breaker of the foregoing type is not the ability to build. up dielectric strength rapidly in the gas space previously occupied by the arc, but rather, it is the ability to hold voltage over the parallel creepage surfaces forrned cy the ceramic material from yw'l'ich the insulating plates are made.

Due to the intense heat generated by arcs, even highly refractory insulating materials may become conducting when electrical arcs are applied over their surfaces. Many ceramic ren fractories which are normally goed electrical inm sulators may decompose or dissociate under ing conditions whereby a portion segregates or volatilizes and the residue becomes electrically conducting. At the instant at which interrup" tion taires place, the surfaces of splitter platesl have just been exposed to arc temperatures of, perhaps, several thousand degrees centigrade. When the dielectric strength of the adjacent to these plates starts to build up, voltage is iin pressed across the highly heated surface current 'flows on the surface, generatinD heat. lf the surface was so hot initially, or the iin-- pressed Voltage is .so high that this heat is genn erated more rapidly than it :is dissipate", then the surface temperature wl rise and it will becorrie even more co 1cl and cause a failure in operation of the l seeker.

We `have found that an unexpected nient in electrical characteristics can be obtained by making the insulating plates 21 from a ceramic refractory composed of le 'it 85% by vwegl'it of sillimanite, which has really good. electrical characteristics at high temperatures as occur adjacent to electrical So-called silliinanite refractorics may be coinposed of one or more of the sillinianite group oi aluminisilicate minerals: particularly andalusite, lryanite, and sillimanite. We have obtained particularly good results with plates rnade of andalusite` The chemical formula for all of these minerals is Al2O3.SO2. Each of them dissociates upon heating at high temperatures to free silica and mullite, 3Al2O3.2SiO2. However, in this case, the products of decomposition (mullite and silica) are good insulators, even at the high temperaturesof electrical arcs. l

As an example, the body of a series of refractory plates was prepared from powdered andalusite admixed with a small amount (2% to 4%) of a powdered borosilicate glass, as a fluxing agent, not execeeding 3% by weight of incidental impurities such as alkali oxides and lime, and from 5% to 8% of refractory type ball clay added for bonding. This body should be fired at a sufliciently high temperature, at least py `rometric cone Il, to bring about at least a partial dissociation to develop mullite crystals which greatly improves the strength, 'thermal resistance, and spalling resistance of the plate. The plates may be fired to provide any desired amount of mullite or even to the extent'that they are composed essentially of mullite and a small amount of free silica which melts at approxin mately 3300 F. This offers the advantage that even though the outermost layers of a plate may be melted by an arc, it will still be a high 'resist-1 ance material which will be beneficial for the reasons set forth.

We will now describe a specific example. in forming 100 pounds of the sillimanite refracftory composition 92 parts of powdered andalusite was admixed with three parts of powdered borosilicate glass composed of 80% SiO2, l2% B203, 7% A1203 and the balance alkali oxides, asr a fiuxing agent and ve parts of refractory ball clay (essentially aluminum silicate) for bonding with a small amount of water to form a plastic mass. Plates were molded from the composition and fired at 2850 F., plus or minus 50 F.

Sillimanite alone may also be used without any bonding 'clay or flux such as glass or lime. ln the case of the pure material the firing temperature is necessarily higher, above 2900" A temporary binder such as dextrin, or polystyrene should be used to bind the particles together to properly mold into plates. During firing the temporary binder is carbonized and burns out.

We have also found that improved performance can be obtained by having the ceramic insulating plates 2l provided with their surfaces grooved, as shown more clearly in Figs. 2 and 3. The grooves 33 in the surface planes of the plates are placed at right angles to the arc, and are sufciently narrow and deep that the bottoms of the grooves are not directly exposed to the arc. The 'creepage path in parallel with the aro is then of alternate bands of hot and cold materials, the resistivity of the cold bands being very high. This means that even after a heavy current interruption, the surface over which creepage would take place, as previously described, is. so completely broken up by these relatively cold bands that breakdown will not occur due to leakage, and full advantage can be taken of the dielectric recovery of the gaseous arc space. Another advantage will be realized from a struc-i ture of plates as described, Such a structure will have a higher interrupting emcien-cy where interrupting efficiency is defined as Max. int. voltage Arc voltage Arc voltage is largerly due to extraction of heat .from the arc.VVV 1t isevident that we have raised the maximum Vvoltage interrupting ability without altering the structure in such a manner as to increase the heat extracted. Lower arc voltage for a given interrupting voltage is an advantage inasmuch as excessive arc voltage is inclined to produce switching surges.

This feature of the groove construction is applicable to insulating plates regardless of the material from which they are made, sillima-nite refractory being preferred, but Zircon porcelain, asbestos lumber, or any other refractory mal terial being improved by such grooving.

In a particular instance, the grooves 33 were 1%; inch deep and were 1% inch apart between their centers. The width of the bottom of the groove was als inch, and the grooves 33 extended approximateli7 3X1 inch above the top of the upper end 3f) of the slot 2S, as shown more clearly in Fig. 2. The grooves 33 extended approximately 1 inch to one side of the slot 28, as shown in Fig. 2, and the distance between the plates 2l was apn proximately 1A; inch, with the plates 21 being substantially 1/4 inch in thickness. The total width of the plates 2l was substantially 31A? inches. The lateral distance between the upper ends of the offset slots 30 was substantially l inch.

Figs. 4 6 illustrate a further embodiment of our invention. This embodiment illustrates the use of our invention in an arc chute 4l of the type consisting of two

wall members

42, 43, each of which has projections or fins 44, 4E which interleave with the fins or projections of the opposite wall member. In other words, upon the assembling of the two

wall members

42, 43. the arc is made to assume a serpentine or sinuous path as it moves upwardly and outwardly through arc chute 4l, as viewed in Fig. 5. It will be noted that the lower ends of the

fins

44 and 45 are chamfered or tapered as at 46, 41 so that the arc is made to gradually assume its sinuous path as it moves upwardly along the

projections

44, 45 in its upward movement through the arc chute 4|.

Preferably a suitable transverse magnetic field set up by blowout structure isutilized in forcing the arc upwardly through the arc chute 4|. The

wall members

42, 43, together with their integrallly formed projections or

fins

44, 45 are formed of the sillimanite material hereinbefore referred to. Also preferably, the two sides of each fin or

projection

44, 45 have formed thereupon the longitudinally extending grooves 48, as more clearly shown in Fig. 6.

As hereinbefore referred to, when the arc is moved upwardly through lthe arc chute 4| and is made to assume a sinuous form, the longitudinally extending grooves or irregularities 48 form a lengthened creepage path in parallel with the arc to thereby prevent reignition of the arc after a current Zero. As previously explained, the bottoms 48d of the grooves 48 are much cooler than the top plate surface and hence the material has better electrical breakdown characteristics.

Although we have shown and described specic structures and material, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the appended claims.

We claim as our invention:

l. yA circuit interrupter of the air-break type including a plurality of closely spaced plates of insulating material having tapered slots provided therein, the tapered portion of the slot in each plate being offset from the center line of the plate and the plates being alternately assembled with the tapered ends of the slots to the right and to the left of the center line to form a zigzag arc passage, means for establishing an arc, the arc moving within the several slots and into the zigzag arc passage, and a plurality of longitudinally ex tending grooves on at least one side of each of a plurality of plates adjacent the slot therein to form upon assembling a lengthened creepage path in parallel with the arc after it has assumed a zigzag configuration near the closed ends of the slots.

2. A circuit interrupter of the air-break; type including a plurality of closely spaced plates of insulating material having tapered slots provided therein, the tapered portion of the slot in each plate being offset from the center line of the plate and the plates being alternately assembled with the tapered ends of the slots to the right and to the left of the center line to form a zigzag arc passage, means for establishing an arc, `the arc moving within the several slots and into the zigzag arc passage, and a plurality of longitudinally extending grooves on both sides of each plate adjacent the slot therein to form upon assembling a lengthened creepage path in parallel with the arc after it has assumed a zigzag con figuration near the closed ends of the slots.

3. A circuit interrupter including a plurality of spaced plates, means lfor establishing an arc and-moving the arc against the edges oi the plates, and the plates being composed of a sillimanite refractory composed oi at least 85% of a mineral composed of .Al2Oz.SiO2.

4. A circuit interrupter including means i'or establishing an arc, an arc chute having insulate ing portions aga-inst 'which the arc is moved, and the insulating portions being composed of a refractory composed of at least 85% of at least one aluminosilicate `mineral selected from the group consisting of A12O3-Si0i and BAlZOaIzii).

5. A circuit interrupter of the air-break type including means for establishing an arc, an arc chute having means at least partly of insulating material for causing the arc to assume a sinuous form, and said latter mentioned means having a plurality of grooves extending transversely of the arc to form a lengthened creepage path in parallel with the arc to prevent reignition after a current zero.

6. A circuit interrupter of the air-break type including means for establishing an arc, an arc chute including two side wall members, each havn ing a plurality of outwardly projecting iins, the ins of one wall member closely interleaving with the fins of the opposing wall member, the arc moving into engagement with the nns and theren by being made to assume a sinuous form, and each of a plurality of iins having at least on one side thereof a plurality of longitudinally extend-u ing grooves disposed transversely of the are to form a lengthened creepage path to prevent reignition of the arc after a current zero.

'7. A circuit interrupter including means for establishing an arc, an arc chute including a pair of opposing wall members, each of which has a plurality of outwardly extending iins, the iins of one Wall member interleaving with the ns of the opposing wall member, the arc moving into engagement with the hns and thereby being made to assume a sinuous form, and the fins being. `composed of. a sillimanite refractory corn- 8 posed of at least oi a mineral composed oi AleOaSOz,

8. A circuit breaker of the air-break type including means for establishing an arc, an arc chute for extinguishing the arc having plate means at least partly of insulating material for causing the arc to assume a sinuous form, the plate means having a plurality of grooves extending transversely of the arc to form a lengthened creepage path in parallel with the arc to prevent reignition after a current zero.

9. A circuit interrupter of the air-break type including means for establishing an arc, an arc chute for extinguishing the arc having plate portions at least partly of insulating material for causing the arc 'to assume a sinuous form, at least some of the plate portions on at least one side thereof having a plurality of grooves extending transversely of the arc to form a lengthened creepage path in parallel with the arc to prevent reignition after a current zero.

l0. A circuit interrupter of the air-break type including a plurality of closely spaced plates of insulating material having tapered slots provided therein, the tapered portion of the slot in each plate being onset from the center line of the plate and the plates being alternately assembled with the tapered ends of the slots to the right and to the leit of the center line to form a zigzag arc passage, means for establishing an the arc moving within the several slots and into the zigzag arc passage, and a plurality of longitudinally extending grooves in the surface plane oi at least one side of at least some of the plates adjacent the slot therein to form upon assembling a lengthened creepage path in parallel with the arc after it has assumed a zigzag coniiguration near the closed ends of the slots.

ll. n circuit interrupter of 'the air-break type including a plurality of closely spaced plates of insulating material having tapered slots provided therein, the tapered portion of the slot in each plate being offset from the center line of the plate and the plates being alternately assembled with the tapered ends of the slots to the right and to the left of the center line to form a zigzag arc passage, means for establishing an arc, the arc moving within the several slots and into the zigzag arc passage, and a plurality of longitudinally extending grooves on both sides of at least some of the plates in the surface planes of such plates adjacent the slot therein to form upon assembling a lengthened creepage path in parallel with the arc after it has assumed a zigzag configuration near the closed ends of the slots.

l2. A circuit interrupter of the air-break type including means for establishing an arc, an arc chute having plate means at least partly of insulating material for causing the arc to assume a sinuous form, the plate means having a plurality of grooves in the surface planes of the plate means extending` transversely of the arc to forni a lengthened creepage path in parallel with the are to prevent reignition after a current zero.

13. A circuit interrupter of the air-break type including means for establishing an arc, an arc chute having plate portions at least partly of insulating material for causing the arc to assume a sinuous form, at least some of the plate portions on at least one side thereof having a plurality of grooves in the surface planes of such plate portions extending transversely of the arc to form a lengthened creepage path in parallel with the arc to prevent reignition after a current zero.

14. A circuit interrupter of the air-break type including means for establishing an are, an arc chute including tWo side wall members each having a plurality of outwardly projecting fins, the ns of one Wall member closely interleaving with the iins of the opposing Wall member, the arc moving into engagement with the iins and thereby being made to assume a sinuous form, and at least some of the fins having at least on one side thereof a plurality of longitudinally extending grooves in the surface planes of the fins disposed transversely of the arc to form a lengthened creepage path to prevent reignition of the arc 15 lil References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 6, page 458; Longmans, Green & Co., N. Y., 1925.