US3909765A

US3909765A - Fused vacuum interrupter

Info

Publication number: US3909765A
Application number: US449265A
Authority: US
Inventors: Edwin A Link
Original assignee: RTE Corp
Current assignee: Cooper Power Systems LLC
Priority date: 1971-10-21
Filing date: 1974-03-08
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

A high voltage high current vacuum fuse having a pair of conductive members supported in a spaced relation within a dielectric housing and shielded by a condensation shield, the conductive members being spaced to provide a gap of sufficient length to interrupt current and being interconnected by a fusible link, the fusible link being of a minimum diameter to provide a minimum volume of fusible material and the conductive members having heads of maximum cross sectional area to provide condensation surfaces of large mass to produce immediate condensation of the vapor produced on fusing of the link. One or both of the conductive members can be biased to increase the gap on fusing of the link.

Description

United States Patent Link 14 1 Sept. 30,1975

[ FUSED VACUUM INTERRUPTER Fri/nan Exumiltel.l. D. Miller l l nvcn or Wm n Au Q a is Assistant E.\'amu1erFred E. Bell Assignccr RTE p i WllukCShlL Attorney, Agent, or FirmRonald E. Barry [22 Filed: Mar. 8, 1974 1211 Appl. No.: 449,265 [57] ABSTRACT v A h' h a h' Related Us. Application Dam 1g voltige igh current vacuum f'use having a pair of conductlve members supported in a spaced relatlon [60] Division of Ser. No. 191205. Oct. 21 1971. which is a continuation-in-part of Ser. No. 18.868 March 12. 1970 abandoned.

within a dielectric housing and shielded by a condensation shield, the conductive members being spaced to provide a gap of sufficient length to interrupt current and being interconnected by a fusible link, the fusible 7 [52] Cl 337/159 "00/144 0 6 link being of a minimum diameter to provide a mini- 51 I t Cl 2 H01" 85704 mum volume of fusible material and the conductive i 166 790 members having heads of maximum cross sectional 1 le 0 earc 6 B 5 area to provide condensation surfaces of large mass to produce immediate condensation of the vapor produccd on fusing of the link. One or both of the con- [56] References cued ductive members can be biased to increase the gap on UNITED STATES PATENTS fusing of the link 2,694,124 11/1954 Laing et a] 337/166 x 3.244.839 4/1966 Albright 337/159 x 3 Clam, 2 Drawmg Flgures 40 55 f 4 47 54 1'1 /7 I I l x I I I I I I 1' '1 FUSED'VACUUM INTERRUPTER r Related; Application This application" is a divis ion' ofrriy' co'pending-USL application Ser; No; 191,205 and entitled Vac\.fum=In-= ter'rup't'er l filed 'on Oct. 21,1971 which is acoritinuation-in-part of my application Ser. No. 18,868 entitled Vacuum Fuse, filed on Mar. 12, 1970 and nowabandoned H BACKGROUND oFIHEiNv NTiou I Vacuum fuses generally have been-provided with'a fusible'link which isconhectedto conductive members located at each end of the fuse. =The fuses rn'ustbeof sufficient cross section t'o'carry normal cu'rrentJThe volume of the fuse" because of its lengthis substantially large and on interruption will produce a substantial amount of vaporized material resulting in'anincrease in pressure between th'e"'contactswhieh might'beeven higher than atmospheric. Condensation shields have been provided to promoterapid eondensation of vaporized material andto mask the inside surface-of the dielectric housing'so that condensed material cannot be deposited on the insidesurfaee ofthe housing. However,'it has been found that due to the l-ar gemass of the fusible element, themomentarywincrease in 'pres'sure produced on fusing of t he'element isla-rge'en'o'ugh to produce an arc plasma sufficient-to support an'arclong enough to"cause an explosive condition in the fuse; l i 1; UM R -Q TH INVEN ON The 'vacuum'fuse of the present inventionminimizes the amount of fusible material in the fuse link while-still providing a sufficient gap between theuconductive members to interrupt ourrentza l'hisis achieved by providinga pair of conductive members-having a substantially large mass within a dielectric housing with the surfaces of the conductive members located in azspaced relation within the housing andconnected by a single fusible link of short length and minimum cross'section. Thelarge mass of the conductive members provides a cooling surface. immediately. adjacent the fusible link for-condensing the vaporizedsfused material-The immediate condensation of the vaporized fused material minimizes the possibility of establishing an arc plasma between the conductive members which could prolong the time of arc interruption.

DRAWINGS FIG. 1 is a side view in section of one form of the invention having a single fusible link interconnecting a pair of stationary conductive members; and

FIG. 2 is a side view in section of another embodiment of the invention showing a single fusible link interconnecting the stationary conductive members and movable members.

DETAILED DESCRIPTION The vacuum fuse of the invention shown in FIG. 1 is a one-shot type fuse generally used in high current high voltage networks. The fuse 10 generally includes a hollow cylindrical housing or casing 12 formed of porcelain, glass or glass ceramic. A cylindrical condenta'lliematei'ialsuch as Ko'var. Y

"The housing 12 is evacuated by means of a tube '22 seale'din an op ening 2 1 provided in one'of' the end' walls 1'8J'Air'is withdrawn from the housing by any co ventiohalrrieans' to produce" a vacuum and tube 22 is criirnped to' se al "the housing 12. "It' is generally understood in a vacuum'iri'terrupting device that the pressure shbuldlb' e reducedsufficiently'to place the gas in a state of molecular flow, "Molecular flow refers to the Knudsen number determined by the ratio of the mean free h of gas molecules to the radius R of a cylindrical tube. when the mean free path L to "R is larger than 1,? considered to be molecular. The gaseous medium in vacuum interrupting devices is usuallyiin the molecular flow range. However, when currents are interrupted the pressure of'the gas in sation shield 14 is mounted within the casing 12 by 65 the arc/column: confined in the space between the contacts be evenhigher than atmospheric. This high p'ressureiriust be reduced very rapidly as the gas diffuses into the volume of the enclosure. Since the arc should not last any longer than half acycle, the pressjur e of the arccolu mn between the contacts should be kept the, limit that permits interruption. This limitis generally recognized to be 10 torr.

; Inaccordance with the invention, the cross section of the ends heads26 ofthe conductive members 16 are large with riespectto the cross sectional area of the fusible element 20. In t his regard, the volume of the fusible,elem ent 29 is kept to a minimum with respect to thevolumetric space between the surfaces of the ends 26 of. the, conductive members 16 in order to interrupt currentin a cycle system assoon as the current passes throughzero. It should be noted thatif. the current continuesto arcfor one or more cycles, an explosive condition will exist within the fuseas a result of the rapid .increase of pressure within the fuse.

The volumeof the fusiblelink is determined by the cross sectional area and the length of the link. The cross sectional area determines the ampere continuous and the length determines the withstand voltage after break. The rate of condensing of the metal vapor on fusing of the link determines the interruption ability, i.e., ampere fault and voltage. Therefore, to increase the rate of condensing of the metal vapor, the cross sectional area of the ends of the conductive members must be increased and/or the amount of vaporized material decreased.

For example, in a ISKV system the fusible link 20 should have a length of approximately /2 inch. The cross sectional area of the ends 26 of the conductive members 16 should be made at least 5 times larger than the cross sectional area of the fusible link. The cross sectional area is determined by the anticipated continuous current.

With this arrangement, a large cooling surface 26 is provided on each side of the fusible element 20. When a short circuit current occurs, the fusible element 20 will vaporize and will immediately condense on the surface of the ends 26 of the conductive members 16. Any

vaporizable material which diffuses outwardly from the space between the ends 26 of the conductive members higher KVs. As seen in FIG. 2, the fuse 40 includes a dielectric housing 42 and a condensation shield 44 secured to the housing by a flange 45. A stationary conductive member 46 is supported on one of the end walls 48 and a movable conductive member 50 is supported by a tubular member 52 provided on the other end wall 54. The outer edges 47 of the end walls 48 are hermetically sealed to the housing 42 and the inner edges 55 of the end wall 54 are hermetically sealed to the other end of the housing 42. The

conductive members

46 and 50 have their inner ends 56 spaced a predetermined distance apart. The circuit through the

conductive members

46 and 50 is completed by means of a fusible element or link 58. The relationship between the cross sectional area of the ends or heads 56 and 57 of the

conductive members

46 and 50, respectively, and the cross sectional area of the fusible link 58 is determined as described above.

However, even though the KV rating is larger, the length of the fusible element is maintained the same. This is accomplished by increasing the distance between the

conductive members

46 and 50. In this regard, the movable conductive member 50 is mounted for axial movement in the tubular member 52 which is secured to the end wall 54. The member 50 is biased away from the member 46 by means of the spring 60 which is connected at one end to the movable element 50 and at the other end to the end wall 54. The conductive member 50 is connected into the circuit by means of a flexible electrical conductor 62 which is connected to an external contact 64 provided in the end wall 54.

On fusing of the link 58, the spring 60 will move the conductive member 50 away from the conductive member 46 toward the end wall 54. This movement of the conductive member 50 provides a double function in that the end 57 of the member 50 provides a large mass to condense the vaporized fuse material and increases the gap between the ends 56 and 57 of the

conductive members

46 and 50. Although a spring has been shown for .biasing the. conductive member 50 towards the end wall 54,.other types of biasing means can be used.

I claim:

1. A fusible vacuum interrupter for proecting a high voltage electric circuit, said interrupter comprising:

a sealed dielectric housing,

two electrically conductive members supported in closely spaced relation in said housing, one of said members being movable within said housing,

a fusible element having a length of approximately inch bridging the space between said members, said members having contact surfaces having cross sectional areas greater than 5 times the cross sectional area of the fusible element,

and means for biasing said one movable member away from said other member.

2. A high voltage vacuum fuse comprising:

a housing formed from a dielectric material,

a pair of electrically conductive members supported in a spaced relation within said housing and being operatively connected to a high voltage circuit, one of said conductive members being mounted for movement within said housing,

means for biasing said one of said members away from said other member to increase the gap between the members on fusing of said element, a fusible element interconnecting said electrically conductive members, said conductive members each having cross sectional areas greater than five times the cross sectional area of the fusible element whereby said members are separated on fusing of said element to provide a sufficient gap for are interruption and a large mass for condensing fusible element material on are interruption. 3. The vacuum fuse according to claim 2 wherein said biasing means includes a spring operatively connected to move the movable member away from the stationary member on fusing of the link.

Claims

1. A fusible vacuum interrupter for proecting a high voltage electric circuit, said interrupter comprising: a sealed dielectric housing, two electrically conductive members supported in closely spaced relation in said housing, one of said members being movable within said housing, a fusible element having a length of approximately 1/2 inch bridging the space between said members, said members having contact surfaces having cross sectional areas greater than 5 times the cross sectional area of the fusible element, and means for biasing said one movable member away from said other member.

2. A high voltage vacuum fuse comprising: a housing formed from a dielectric material, a pair of electrically conductive members supported in a spaced relation within said housing and being operatively connected to a high voltage circuit, one of said conductive members being mounted for movement within said housing, means for biasing said one of said members away from said other member to increase the gap between the members on fusing of said element, a fusible element interconnecting said electrically conductive members, said conductive members each having cross sectional areas greater than five times the cross sectional area of the fusible element whereby said members are separated on fusing of said element to provide a sufficient gap for arc interruption and a large mass for condensinG fusible element material on arc interruption.

3. The vacuum fuse according to claim 2 wherein said biasing means includes a spring operatively connected to move the movable member away from the stationary member on fusing of the link.