US2309489A - Electric circuit interrupting device - Google Patents

Electric circuit interrupting device Download PDF

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Publication number
US2309489A
US2309489A US349847A US34984740A US2309489A US 2309489 A US2309489 A US 2309489A US 349847 A US349847 A US 349847A US 34984740 A US34984740 A US 34984740A US 2309489 A US2309489 A US 2309489A
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United States
Prior art keywords
current
voltage
circuit
fusible
interrupting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US349847A
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English (en)
Inventor
Jr Edwin A Williams
Carl L Schuck
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General Electric Co
Original Assignee
General Electric Co
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Filing date
Publication date
Priority to BE446567D priority Critical patent/BE446567A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US349847A priority patent/US2309489A/en
Priority to GB9711/41A priority patent/GB548030A/en
Priority to FR874607D priority patent/FR874607A/fr
Priority to DEA20791D priority patent/DE1003332B/de
Application granted granted Critical
Publication of US2309489A publication Critical patent/US2309489A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
    • H01H85/02—Details
    • H01H85/38—Means for extinguishing or suppressing arc

Definitions

  • the present'invention relates to high voltage .f circuit interrupters of the kind referred to as" current limiting devices because of their ability under severe short-circuit conditions, to limit the short-circuit current to a peak magnitude considerably below that of the prospective or available current which otherwise would be produced.
  • the current interrupting link or agency includes a long fusible conductive section surrounded by an inert refractory material of high dielectric strength, the form, composition and arrangement of which material and conductive section are such that, upon dissipation of the conductive section by severe shortcircuit current, there is inserted into the current path a high resistance which sharply limits the current rise and produces a rapid current decay, resulting in final circuit interruption in an extremely short period of time, not exceeding a half cycle in the case of alternating current.
  • the sudden increase in resistance of the arc path gives rise to transient voltage surges,
  • an interrupting link or agency constructed in accordance with the present inverntion, embodies a plurality of elements in parallel (ICI. 20D- 120) relationship and so arranged that they function successively in a manner to cause insertion of resistance in such amounts and at such rates that there is not produced at any time during the interrupting process, a rate of current decay which will cause a surge voltage peak in excess of a predetermined magnitude.
  • FIG. 1 shows, in longitudinal cross-section, an exemplary form of current limiting circuit interrupting device to which the present invention is applicable;
  • Figs. 2, 3, 4, and 5 show details of construction oi' (iiiferent forms of current interrupting links which embody the present invention and which are suitable for employment in a device such as that shown in Fig. l;
  • Fig. 6 is an enlarged perspective view of a part employed in the constructions of Figs. l, 2, 3, and 4;
  • Fig. 'T is a longitudinal section of one end of a device such as shown in Fig. 1, illustrating the manner of incorporating therein an interrupting linev having elements constructed as shown in Figs. 4 and 5;
  • Fig. 8 is an end View of the core employed in the structures shown in Figs. 1 and 7;
  • Fig. 9 contains diagrammatic representations oi oscillographic curves of current and voltage, respectively, illustrating conditions of circuit interruption as secured with a current limiting device wherein the current interrupting link is of a form old in the art;
  • Fig. 10 contains diagrammatic representations of oscillographic curves of current and voltage
  • the illustrated circuit interrupting device has a tubular enclosing casing 20 upon the 'opposite ends of which are disposed metallic termi- While the casing is'indicated as being constructed of glass, other suitable materials of high dielectric strength, such as porcelain, may be employedif desired.
  • the terminal ferrules are secured on the casing by any suitable form of metaltog1ass seal, indicated at 22, and the outer ends of the ferrules are closed by sealed-n caps 23.
  • an insulating and refractory core 24, extending longitudinally in casing 2G, is provided for the purpose of supporting the long current interrupting link so that the latter may be accommodated in a casing of practical dimensions.
  • the particular interurn spirally wound on the core the form shown in Fig. 2 and includes two elements 25 and 26 in parallel relationship, vhich are described in detail hereinafter. any of the other forms of interrupting links illustrated in the drawings, may be supported the core in a similar manner.
  • the inter of the casing 20 around the core is filled with a granular refractoryT arc-quenching matelial such es sand or pulverized quartz, which high dielectric strength and is substantially inert or nou-gas-producing, at the i, :ely to be encountered during cir- 1 ⁇ hiterruption.
  • a granular refractoryT arc-quenching matelial such es sand or pulverized quartz, which high dielectric strength and is substantially inert or nou-gas-producing, at the i, :ely to be encountered during cir- 1 ⁇ hiterruption.
  • f core 2i has o. plurality of longitudinally .ung fins or ribs which engage the conrs cf the interrupting link only at spaced and serve to maintain the conductors f utwardly from the central body portion o e core.
  • the maximum length of the conductors is embedded in and directly exposed to the arc-quen
  • iinals 3U which are mounted respectively on om. 'te ends of core 2l.
  • suitable u may be employed for purrticular terminals employed in constr 'ion are oi' the improved i supplication Serial No. 347,437, no stent 2,294,132, oi C. L.
  • the embodiment cL Fi current element and is coi4 ble conductor of thin cross-section, which may be of any suitable form and material in accordance with known principles for the construction of lnterrupting elements for current limiting circuit interrupting devices.
  • the conductor 33 of the illustrated construction comprises a. fine silver wire, which is particularly satisfactory for current conduction under normal circuit conditions.
  • Smallbeads or thermal reservoirs 3l of refractory insulating material, surround short sections of wire 33, preferably adjacent the middle thereof, for the purpose of determining the minimum current at which interruption takes place. These thermal reservoirs prevent contact of the enclosed wire sections with the granular filler material and hold in the heat. Thus it is insured that the wire will melt on an overload involving a lower magnitude of current than would be possible with the same conductor without the thermal reservoirs.
  • the voltage element designated 2i in the construction of Fig. 2, comprises two conductors 33 connected at their outer ends to terminals 3
  • each of the conductors 35 is looped through a respective one of the openings 31 in member 33, and the conductors are secured by twisting; as indicated at 38.
  • Member 36 maintains the ends of conductors 35 in spaced relationship so as to provide a gap which is calibrated to lash over at a predetermined voltage. The calibration of the gap is determined in a manner hereinafter pointed out and may vary for interrupting devices of different voltage and current ratings.
  • the gap may be located at the end of a voltage element having one long conductor instead of two serially related shorter conductors. How "er, it has been found that bestresults are ol'itoir. i with the gap located adjacent the middle oi 5 f voltage element illustrated.
  • the form and dimensions ci conductors 35 are determined in accordance with known principles for the construction of fusible ments for current limiting circuit interrupting devices, with certain variations which will be poin j out.
  • conductors 35 are comprised of a material having high electric resistivity and a high temperature coeicient of resist-ance. We have found that a good material for the purpose ls a nickel-chromium-iron alloy known by the trade name Hytemcof although other suitable materials haring the above mentioned characteristics may be employed if desired.
  • the current element embodied in interrupting links constructed in accordance with the present invention may comprise etiher a single unit, such as that designated 25 in Fig. 2, or a plurality of similar units connected so as to provide parallel as shown in Fig. 5.
  • the inual units are designated by the numeral l0 5, they fundamentally the same in unit designated 25 in Fig. 2.
  • ge element may comprise single unit, such as that designated 26 either a in Fig. 2, or may comprise a plurality of similar units connected in parallel branches as shown in lli-isf 4, the individual units 4I of Fig. 4 being of terrupting action is produced with fusible conductors of thin cross-section.
  • the rapid insertion of high resistance also causes a very rapid current decay from b to some point generally designated cv in Fig. 9, after which the current decays somewhat less precipitously and is nally interrupted at d, which corresponds to the zero point of the nor mal circuit voltage.
  • the final interruption of the current is accomplished with minimum disturbance, and takes place within an extremely short period of time which does not exceed a half cycle in the case terruption, as illustrated in the drawings.
  • the described current limiting action is produced under all conditions within the rating of the interrupting device, provided the magnitude of current required to melt and volatilize the fusible conductor is reached before attainment of the peak magnitude of prospective current. Obviously, current limiting action cannot be produced if the peak magnitude of prospective current ls reached before attainment of the mag nitude of current required to melt and volatilize the conductor.v
  • the surge voltage may rise to a crest magnitude which is undesirably high and which may be above the established impulse insulation levels of connected apparatus.
  • the voltage element takes no part in this initial stage of the interrupting process but is conserved, by the gap between the ends ci conductors J5, for most effective operation. during later stages in the interrupting p i.
  • the calibration of the gap in the volti t determines the magnitude to r t "r across the termi- ;ig no
  • the voltage surge f may magnitude considerably beated e.; c in Fig. 9, which would beucit element alone were emplayed.
  • En prac ior any particular interrupting device an is calibrated so as to pre vent the rst voltage surge f from attaining a peak magnitude in excess of the limit, or impulse insulation level, which is predetermined in accordance with the application for which the interrupting device is designed.
  • conductors 35 of the voltage element are brought into the circuit in shunt relationship to the arc lpath formerly occupied by the current element. This occurs at a point such as that indicated at g on the current curve in the upper part oi Fig. 10.
  • the current decag7 immediately subsequent to connection oi' conductors 35 in circuit is less rapid than that represented by the portion b-g on 'the current curve of Fig. offered by conductcrs 35, though high, is less than that of the arc path formerly occupied by the current element.
  • the interval between melting oi the current element and melting of the voltage element is a very important factor in de termining the me nitude of the voltage surge crest. 'if int 10, since the resistance :val is too short, the second as crystala voltage surge will be superimposed upon the first voltage surge peak, resulting in a high surge crest.
  • the time spacing between melting of the current and voltage elements therefore should be such that the second voltage surge is not initiated at or near the peak of the iirst voltage surge, but rather is initiated after the rst voltage surge has fallen to a value approaching the normal circuit voltage.
  • the interval between melting oi the current element and melting of the voltage element usually should be at leastlOO to microseconds.
  • the magnitude of the second voltage surge is determined to a large extent by the delay afforded before melting of the voltage element. Within practical limits, the greater the interval between melting of the current and voltage elements, the smaller will be the peak magnitude oi the second voltage surge. This interval can be controlled by proper calibration of the gap of the voltage element and the melting characteristics of the voltage element. Increasing the length of the gap will delay subjection of the voltage element to the short-circuit current, and thus will delay initiation of heating of the conductive portions of the voltage elements. However, as previously indicated, the calibration of the gap determines the peak of the first voltage surge, so that a limit is reached beyond which it is not desirable to increase the gap spacing.
  • variation in the magnitude of the second voltage peak may be secured by variation in the melting characteris- Itics of the conductive portions of the voltage element.
  • This can be accomplished by employing diiierent resistance materials.
  • a voltage element comprised of a given resistance material does not afford a delay sufiicient to prevent rise of the second voltage surge beyond a predetermined desired limit
  • a voltage element comprised of a different resistance material having such melting characteristics as to provide the required delay.
  • the melting characteristics o! materials having suitable resistance characteristics, comparable to those o! the nickel-chromium-iron alloy Hytemco previously mentionedy may not aord suiilcient latitude under some conditions.
  • Cross-section is used in the sense of total cross-section, of either the single-unit voltage element construction of Fig. 2 or a. pluralunit voltage element construction such as shown in Fig. 4. If, for a given interrupting device, a voltage element of a given cross-section does not produce reduction in the surge voltage crest below the limit predetermined for the application for which the interrupting device is designed, then a voltage element of suiiiciently larger crosssection may be employed to give the desired reduction.
  • ratios of crosssection o! voltage element to cross-section of osseuse ouvrent element falling sommeliers in the range of about 1 to 4, depending upon the rating of tlie particular interrupting device, usually are sufficient to prevent surge voltages in excess of prevailing impulse insulation levels determined for the classes of apparatus with .whioh these current limiting' eiiouit interrupting devices :sie likely to be employed.
  • gap means in series with fusible set ion of said second element to prevent current eonduetion by the letter until the voltsle reaches a predemwuf e iollowing rupture of the iusible section rst elementy und are* uueuohing o@ ble of producing e current limiti-ig eetion ien dissipation o eash oi sold fusible Q'eotions u deim severe -overourrent eondi- C, tions., d usp means being arranged to break domi ef voltage substantially lower than the peak magnitud oi Volto-ge surge .likelyw to ne produced unen sei/ete overcuelent dissipation oi the fusible section @aid :tiret element if the letter d means, tile isf-sible section of seid secon. ele-d ynent 'seeing construeted
  • first element were employed withmeans said second element, said aid second element being desection: e voltage Y e portions hevtween for preventing sai ⁇ conductive portions is subjected to voltage or" predeter- "ude following rupture of the fusible 'st mentioned element, said conhaving high resiste-.nce and c oereture ccecient of resistance 'anu refractory are-quenching ine.- embedding said conductive portions of the e c el element.
  • electric circuit interrupter of the cur- 'riiting t'ype including spaced terminals, a y carrying' element connected between said nels and having a long fusible section, and c, Meguiar inert refractory arc-quenching materlel embedding seid fusible section; a voltage contr-oi element connected between said termiourallel with first mentioned element the crest magnitude of voltage surge dosed upon interruption of severe over-curl. conditions.
  • said control element including two seriallyrelated conductive portions, at least one ol' ⁇ which conductive portions being designed to dissipate prior to dissipation of the other of the conductive portions upon subjection of 'said control element to excess current of large insigni tuile, at least seid one conductive portion having high resistance, seid control element also includen ens providing a gap in series 'with said ⁇ onductive portions for preventing current condu ti hy the control element until the gap is subjected to voltage of predetermil Ad magnitude follo'sdug rupture of the fusible section of said C t element7 and granular inert refractory urcring material embedding said fusible conductive portions of said control element.
  • a pair of terminals means normally providing a first current path of good etivity between said terminals and inclu;- rusllole section which is capable of reducing the current of the system associated with said circuit inter ollowing severe short circult so rapidly as to tend to produce a harmful surge voltage on.
  • an electric circuit interrupter capable of substantially li ing the magnitude of fault our rent flowing therethrough including a. fusible element for normally provldinff a current path having good conductilty through said circuit interrupter, and ineens for limiting the transient voltage surge which results due to the currentlimiting feature of said circuit iuterrupter under severe fault conditions to a predetermined safe value comprising a circuit connected in parallel With said fusible element which normally carries substantially no current but citer fusion of said fusible element und before said voltage surge can exceed said predetermined safe velue carries the fault current through' said circuit interrupter, said l: mmentioned being fusible finally to interrupt the circuit at least 100 micro-seo cfids after the fusion of said fusible element.
  • an electric circuit interrupter capable of substantially limiting the magnitude of fault current flowing therethrough including a fusible element for normally providing a current path having goed conductivity through said clrcuit interrupter, and means for limiting the transient voltage surge which results due to the current-lirniting feature of said circuit interrupter under severe fault conditions to a predetermined safe value
  • a circuit connected in parallel with seid fusible element including 9, plurality of parallel gaps which normally carry substantially no current until alter fusion of said fusible element.
  • an electric circuit interruptor capable of substantially limiting the magnitude of fault current flowing therethrough including a fusible element for horn .liv providing a current path having conduct... t3. through said circulfJ interruptor, and means for limiting the transient voltage surge r h re due to the currentlimiting feature of said 3u-cuit interrupter under severe fault con uic-ns to u predetermined sole value comprising e. circuit connected in 'parallel with said fusible element including a plurality of parallel gaps cf dizlerent spacing which normally carry suhstent' illy no current until uiterffusion of said fusible element.

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  • Emergency Protection Circuit Devices (AREA)
  • Fuses (AREA)
US349847A 1940-08-02 1940-08-02 Electric circuit interrupting device Expired - Lifetime US2309489A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BE446567D BE446567A (US20090192370A1-20090730-C00001.png) 1940-08-02
US349847A US2309489A (en) 1940-08-02 1940-08-02 Electric circuit interrupting device
GB9711/41A GB548030A (en) 1940-08-02 1941-07-30 Improvements in and relating to electric circuit interrupting devices
FR874607D FR874607A (fr) 1940-08-02 1941-07-30 Perfectionnements aux coupe-circuits
DEA20791D DE1003332B (de) 1940-08-02 1942-01-13 Hochspannungsschmelzsicherung

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US349847A US2309489A (en) 1940-08-02 1940-08-02 Electric circuit interrupting device

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US2309489A true US2309489A (en) 1943-01-26

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US349847A Expired - Lifetime US2309489A (en) 1940-08-02 1940-08-02 Electric circuit interrupting device

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US (1) US2309489A (US20090192370A1-20090730-C00001.png)
BE (1) BE446567A (US20090192370A1-20090730-C00001.png)
DE (1) DE1003332B (US20090192370A1-20090730-C00001.png)
FR (1) FR874607A (US20090192370A1-20090730-C00001.png)
GB (1) GB548030A (US20090192370A1-20090730-C00001.png)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3835431A (en) * 1969-09-23 1974-09-10 English Electric Co Ltd Electrical fuse

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3835431A (en) * 1969-09-23 1974-09-10 English Electric Co Ltd Electrical fuse

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Publication number Publication date
BE446567A (US20090192370A1-20090730-C00001.png)
DE1003332B (de) 1957-02-28
FR874607A (fr) 1942-08-13
GB548030A (en) 1942-09-22

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