US2708699A - Finger contact structure for circuit interrupting device - Google Patents

Description

May 1955 G. E. JANSSON 2708699 FINGER CONTACT STRUCTURE FOR CIRCUIT INTERRUPTING DEVICE Filed Jan. 2, 1952 O O O United States Patent FINGER CONTACT STRUCTURE FOR CIRCUIT INTERRUPTING DEVICE Gustav E. Janssou, North Quincy, Mass., assignor to Allis-Chalmers Manufacturing Company, Milwaukee,

Wis.

Application January 2, 1952, Serial No. 264,381

4 Claims. (Cl. 200146) This invention relates to circuit interrupting devices and more particularly to contact structures for use in connection therewith.

In accordance with the invention claimed a circuit interrupting structure is provided which employs a switch comprising a pair of spaced movable contact members, a pair of spaced stationary contact members, and a plurality of pairs of bridging elements. The bridging elements may be resiliently mounted on the stationary contact members and engage the movable contact members when the switch is in circuit closed position. The movable contacts may comprise a relatively long blade contact and a parallelly arranged relatively short blade contact. Both blade contacts serve as current carrying contacts during part of a circuit interrupting operation, and the relatively long blade contact serves as an arcingcontact during another part of the circuit interrupting operation.

It is, therefore, one object of the'present invention to provide a new and improved arc interrupting device.

Another object of this invention is to provide a new and improved contact interrupting structure.

A further object of this invention is to provide a contact structure in which the current paths through the structure are shifted in a new and improved way during circuit interrupting operation to eifectively'elongate and extinguish the arc.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing partly in elevation and partly in cross section of a fluid blast circuit breaker embodying the present invention;

Fig. 2 is an enlarged partial view in cross section of the embodiment illustrated in Fig. 1- taken along the line II-II;

Fig. 3 is an enlarged partial cross sectional view of the embodiment illustrated in Fig. 1 taken along the line III-III; and

Fig. 4 is an enlarged partial cross sectional view of Fig. 1 taken along the line IV-IV. 1

In accordance with the inventionclaimed, the cross blast type air blast circuit breaker 5 shown in Fig. 1 cmploys a fixed contact structure 6 and a movable pivoted blade-like contact structure 7. The fixed contact structure 6 comprises a plurality of spaced stationary contact members 8 (more clearly shown in Figs. 2' and 33) mounted on a terminal structure 33 and a plurality of pairs of bridging elements or contact fingers 9 resiliently mounted on the stationary contact members 8 by means of a plurality of springs Iii. Each pair of bridging elements 9 is arranged to contact one of the stationary contact members 8 and is resiliently biased by'sprin'gs 10 into wiping electrical engagement with the movableblade-like contact structure 7 when the switch is in circuit closed position.

The blade-like contact structure 7 comprises a pair of spaced movable contact members 11 and 12 secured to a movable member 13 which is pivotally mounted at 14 on a second terminal structure 34. Contact member 12 is arranged substantially parallel with contact member 13 and is longer and wider than contact member 13 (as clearly shown in Figs. 2, 3 and 4). As shown in Fig. 2 contact 12 is provided with an arcing tip 15 made of suitable conductive rnaterial which extends beyond the end of contact 12. A bridging element 16 cooperating with tip 15 likewise extends beyond the other bridging elements 9. Thus tip 15 makes contact with the bridging element 16 first in contact closing direction and breaks contact last with the bridging element 16 in contact opening direction.

Although in general, circuit breakers of the type considered in Figs. 1, 2, 3 and 4 are provided with a plurality of similar pole structures, one for each phase of a polyphase electric circuit, only one such pole structure is shown in the drawing and the circuit breaker will be described in detail as if. it were of the single pole unit type.

The movable contact structure 7 is suitably connected to an actuating mechanism (not shown) through a connecting rod 17 for operating the movable contact between closed and open circuit positions.

For extinguishing the are formed between the contacts when a power circuit connected thereto is opened, an insulating arc extinguishing structure 18 is arranged with respect to the contacts so that the are is drawn at the entrance of the structure directly opposite a gas blast supply conduit 19. The conduit 19 is suitably connected through a blast valve (not shown) to a source of compressed gas, such as air, comprising for example a storage tank and compressor equipment (not shown).

The arc extinguishing structure may, for example, define a double barreled arc chute 20 comprising a first blast passage 21 for interrupting relatively high currents and a second blast passage 22 arranged parallel with and spaced from passage 21 for interrupting relatively low currents. The blast passages 21 and 22, as illustrated in Fig. 3, have substantially uniform cross sections which may be rectangular or circular.

Aninsulating blast divider 23 is arranged between the gas supply conduit 19 and the arc chute 20 for distributing the blast from the point where it arrives in highly concentrated form through the narrow blast supply conduit 19 to an arc chamber provided for enclosing the are upon inception thereof. The are chamber comprises arcing zones 24 and 25 which are spaced and situated at the upstream end of the double barreled arc chute 26. The blast divider comprises a funnel shaped portion 26 mounted immediately adjacent the supply conduit 19 and a pair of nozzles 27 and 28 which diverge from the diverging end of portion 26 toward chute passages 21 and 22.

The sides of the funnel shaped portion 26 diverge at such a rate that the air expansion within the funnel is limited to the required minimum. The common axis 30 of supply conduit 19 and of funnel shaped portion 26 of blast divider 23 is situated only slightly to the right of axis 31 of the first blast passage 21 of arc chute 20. Thus, the air blast reaching the downstream end of funnel shaped portion 26 may pass into nozzle 27 with little restriction.

Nozzle 27 comprises an inlet portion and an outlet portion. The inlet portion may be asymmetrical and the outlet portion symmetrical. Nozzle 27 may have a zone of minimum cross sectional area between the upstream andthe downstream ends thereof and the walls thereof may converge more rapidly on the upstream end thereof than they diverge on the downstream end thereof, thus providing a well defined point of maximum flow velocity where the rate of deionization of the arc path is high and the rate of fluid expansion downstream from the point of maximum flow velocity is controlled. The outlet portion of nozzle 27 forms with the wall of the first blast passage 21 a circular air pocket or gap 32.

Nozzle 28 comprises an inlet portion and an outlet portion. The inlet and outlet portions may provide an oblong cross sectional area. The width of nozzle 28 may be constant throughout its length and is preferably greater than the width or" nozzle 27 at its narrowest point. Nozzle 28 provides a zone of minimum cross sectional area between the inlet and outlet ends thereof.

As illustrated in Figs. 1 and 4 the fixed contact structure 6 projects substantially to the longitudinal axis of nozzle 27 and is therefore subjected to an intense air blast upon operation of the arc extinguishing structure.

The walls of the funnel shaped portion 26 of the blas divider 23, as illustrated in Fig. l, define passages 35 therethrough which accommodate the movable sickle shaped blade contact members 11 and 12. These walls closely surround contacts 11 and 12 and control the escape of compressed air and are products through passages 35 into blast passages 21 and 22. Passages 35 are provided with a plurality of transversal grooves 36 which tend to establish eddies in the small flow of air and are products escaping through passages 35 to atmosphere. These eddies, in turn, tend to minimize the rate of that flow.

A pair of probe electrodes 37 and 38 may be mounted within blast passages 21 and 22, respectively, for aiding arc extinguishment. Electrode 37, as illustrated in Fig. 2, may comprise a rectangular portion 39 of refractory metal or alloy which is mounted to extend across the full width of the first blast passage 21 at the downstream end of nozzle 27. A current limiting resistor 40 interconnects electrode 37 and the multiple finger contacts of the fixed contact structure 6, thus lowering the value of the arc current at a predetermined time during arc extinguishment. Electrode 38 may comprise a rectangular portion 41 of refractory metal or alloy which is mounted to extend across the full width of the second blast passage 22 at the downstream end of nozzle 28.

The circuit breaker illustrated in the drawing is shown with the cooperating contacts in the closed circuit position. An opening operation is initiated by admission of gas under pressure to supply conduit 19. The further flow of such gas through passages 35 of funnel-shaped portion 26 of blast divider 23 is at first impeded by contact members 11 and 12, which obstruct the passages 35. Actuation of the connecting rod 17 moves'movable member 13 and contact members 11 and 12 toward the right to open the electric circuit.

While the contact members 11 and 12 remain in electrical contact with the bridging elements 9 both members 11 and 12 serve as current carrying contacts. However, as member 13 is actuated to circuit open position, member 11 disengages from bridging elements Q before member 12. Therefore, at first members 11 and 12 both serve as current carrying contacts and then member 12 only serves as current carrying contact during a circuit opening operation. Upon further movement of members 11 and 12 in circuit opening direction the arcing contact tip 15 of member 12 disengages contact bridging element 16 and draws an arc therebetween.

As the blade contact member 12 is separated from the fixed contact 6, an arc is drawn across the arcing zone 24 leading to the first blast passage 21 and substantially concurrently therewith a path is opened for a blast of gas of high intensity through the supply conduit 19 and nozzle 27 of blast divider 23 to the first blast passage 21. This of blast divider 23 are uncovered and part of the arc is driven or looped from zone 25 into blast passage 22 by the blast from nozzle 28.

The funnel shaped portion 26 of blast divider 23 forms a blast duct, the side walls of which diverge at a rate such that the air expansion within the blast duct is limited to a predetermined minimum value. The blast therefore reaches the arcing zone at a high pressure that has a strong tendency to overcome the back pressure produced by the heat generated by the arc. The common axis of conduit 19 and funnel shaped portion 26 of blast divider 23 is situated slightly to the right of the axis of the first blast passage 21 of arc chute 20. This is conducive to such a distribution of the blast of air that most of it is caused to escape through the first blast passage 21 which is situated immediately adjacent the stationary finger contacts 9 while only a minor portion of the blast is caused to escape through the second blast passage 22 which is situated at a point remote from the stationary finger contacts 9.

This concentration of the blast in the form of a high intensity stream on the stationary arcing contact structure 6 causes an intense deionization of the arc path at the point where a reignition is most likely to occur. The concentration of the blast upon arcing zone 24 and the first blast passage 21 causes a rapid rise of the resistance of the portion of the are situated at the upstream end of the blast passage 21. The are rises and comes in contact with probe electrode 37. The section of the arc which is shunted by resistor 40 interconnecting the fixed finger contact structure 9 with the probe electrode 37 arranged in the first blast passage 21 will be rapidly extinguished and replaced after the first current zero by current through the resistor 40. From then on in the interrupting cycle, the task is limited to interrupting a resistor limited arc current of lower intensity and this may be achieved either at the upstream end of blast passage 21 or at the upstream ends of the first and second blast passages 21 and 22, respectively.

By providing rectangular shaped probe electrode portions 39 and 41 extending across the full width of blast passages 21 and 22, respectively, are arc when driven into passages 21 and 22 cannot bypass the electrodes 37 and 38 without being engaged by them. Thus, the full arc extinguishing effect of the probe electrode is assured.

The intensity of the blast of gas necessary to interrupt a resistor limited current of low intensity is much lower than that necessary to interrupt a higher arc current. Therefore, a blast of gas of relatively low intensity is provided through blast passage 22 for interrupting lower cur rents. The lower intensity of such blast results both from the division of the blast into two streams through nozzles 27 and 28 and of the arrangement of nozzle 28 out of axial relation with supply conduit 19, whereby the momentum of the blast forces it to flow principally blast of gas provided by nozzle 28.

blast includes substantially all the gas being supplied through conduit 19, and drives or loops the are from zone 24 into passage 21. Frequently the arc is interrupted in the first blast passage by the blast of gas flowing through through nozzle 27.

If the arc is not interrupted in blast passage 21 by the high intensity stream provided by nozzle 27 of blast divider 23 the resistor limited current is then interrupted in blast passage 22 by a lower intensity Gap 32 formed by the outlet portion of nozzle-27 and the upstream portion of blast passage 21 forms a circular air pocket which is not likely to be contaminated by are products and thus tends to preclude an electric breakdown between the first and second blast passages 21 and 22, respectively.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departingfrom the spirit of the invention or from the scope of the appended claims. 7

It is claimed and desired to secure by Letters Patent:

1. A switch comprising in combination a pair of parallel flat movable contact members facing each other along their widest surfaces, a pair of spaced stationary contact members, and a plurality of pairs of bridging elements for providing electrical connection between said movable and said stationary pairs of contact members when said switch is in circuit closed position, both of said movable contact members acting as current carrying contacts during part of a circuit opening operation and only one of said movable contact members acting as an arcing contact during another part of the circuit opening operation.

2. A switch comprising in combination a pair of parallel fiat movable contact members facing each other along their widest surfaces, 21 pair of stationary spaced contact members, a plurality of pairs of bridging elements, each pair of said bridging elements arranged to contact one of said stationary contact members, and resilient means for biasing said bridging elements into wiping electrical engagement with said movable contact members when said switch is in circuit closed position, both of said movable contact members acting as current carrying contacts during part of a circuit opening opera- 1.

tion and only one of said movable contact members acting as an arcing contact during another part of the circuit opening operation.

3. A switch comprising in combination a pair of spaced stationary contact members, a pair of parallel flat movable contact members facing each other along their widest surfaces, a plurality of rows of pairs of bridging finger contact elements resiliently mounted on said stationary contact members for providing electrical connection between said stationary and movable contact members when said switch is in circuit closed position, each of said movable contact members engaging a different row of bridging elements, said movable contact members comprising a member which breaks electrical contact with one row of said bridging elements last remaining in circuit during a circuit opening operation to form the interrupting arc.

4. A switch comprising in combination a pair of spaced stationary contact members, a movable contact member, a plurality of rows of pairs of bridging finger contact elements resiliently mounted on said stationary contact members for providing electrical connection between said stationary and movable contact members when said switch is in circuit closed position, said movable contact members comprising a relatively long flat blade contact and a substantially parallelly arranged relatively short fiat blade contact, said blade contacts facing each other along their widest surfaces, said relatively long blade contact making contact with one row of said contact elements before said relatively short blade contact makes contact with another row of said contact elements in a circuit closing operation and breaking contact last with said one row of contact elements in circuit opening operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,898,135 Massey Feb. 21, 1933 2,243,567 Linde May 27, 1941 2,347,052 Hobson Apr. 18, 1944 2,349,681 Slepian May 23, 1944 2,351,426 Healis June 13, 1944 2,376,818 Rubel May 22, 1945 2,571,864 Graybill Oct. 16, 1951 2,600,211 Cushing June 10, 1952

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