GB2140972A

GB2140972A - Vacuum switch contacts

Info

Publication number: GB2140972A
Application number: GB08408289A
Authority: GB
Inventors: Edward F Veverka
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1983-03-31
Filing date: 1984-03-30
Publication date: 1984-12-05
Also published as: CA1234856A; NL8401005A; JPS59186219A; GB8408289D0; DE3411784A1

Abstract

A contact structure for a vacuum circuit interrupter is described in which a ring-shaped contact member 30 is secured to the rim of a cup-shaped portion 20 of a support member 12. Helical grooves may be provided in the wall of the cup-shaped portion 20 of the support member to cause rotation of an arc around the ring-shaped contact. A non-magnetic reinforcing means 28 is provided to support the ring-shaped contact member 30 from the support member independent of the walls of the cup, so as to prevent deformation of the walls of the cup when a pair of the contacts forcefully engage each other during a circuit interrupter closing operation. <IMAGE>

Description

SPECIFICATION Contact structure for vacuum circuit breaker Field ofinvention This invention relates, in general, to vacuum circuit interrupters, and more particularly, to a contact structure for use in a vacuum circuit interru pter.

Background ofinvention Vacuum circuit breakers or interrupters generally include an evacuated housing or chamber enclosing a pair of circuit making and breaking contacts which are assembled within the housing in such a manner as to permit their movement into and out of engagement with each other. When utilized to interrupt current flow, the contacts are moved apart, thereby initiating an arc between the separating contacts. The arc initiated between the facing contact surfaces heat the contact surfaces to a relatively high temperature. Should this relatively high temperature exist when a circuit is reestablished throught the vacuum interrupter contacts by bringing them into engagement, the possibility of established a weld between the two contact surfaces arises.Such contact welds are objectionable, wherein they interfere with the proper and easy disengagement of the contacts when it is desired to again interrupt or open the electrical circuit of which the vacuum interrupter contact form a part.

Numerous improvements in the design of vacuum circuit interrupters have been disclosed for reducing or avoiding unobjectionable contact welds. It is obviously desirable to form the contact engaging surfaces of a material which will minimize the possibility of a weld. It has also been etermined that the possibility of a weld being formed can be reduced by causing the arc to rapidly move across the surfaces of the contacts. The rapid movement of the arc will result in lower contact temperature, thereby reducing the thermoelectron emission by reducing the quantity of electrode material vaporized and by providing a greater dispersion of that electrode material which is vaporized, so as to provide a faster dielectric recovery in the gap between the contacts.The formation of slots in the contact and/orthe contact supporting member, in conjunction with the magnetic forces generated by the current to be interrupted will cause the arc to be rotated around and radially outward on the contact surfaces. Numerous ways of forming these slots have been shown in issued U.S. Patents. In vacuum circuit interrupters utilizing disk shaped, rather than ring-shaped contacts, the spiral grooves have been formed in the contact surface as shown in U.S.

Patents 3,327,081 -Pflanz and 3,462,572 - Sofianek. In the cae of cup-shaped contact, the grooves have been formed so as to extend from the contact engaging surface, spiraling through the contact supporting wall, to the supporting base of the contact structure. Patent documents showing cupshaped contacts with grooves of this type are U.S.

Patent 3,089,936 - Smith, 3,836,740 - Hundstad and British Patent Application 2,002,1 77A published February 14, 1979. With respect to cup-shaped contacts it has also been suggested that the contact surface be continuous, with the spiral grooves only being formed in the supporting structure. This type of construction is shown in U.S. Patent 4,267,416 Paulus.

The preferred material for the contact structure in a vacuum circuit interrupter is generally copper or a copper alloy. The copper or copper alloy are preferred wherein they have both high electrical and high thermal conductivity. The copper or copper alloy further has good dielectric strength, which derives from its own high tensile strength. However, wherein it is necessary during assembly to subject the contact structure to a brazing cycle, which may involve temperatures in the order of 800"C, the copper or copper alloy parts lose their temper, thereby becoming relatively soft. In the softened condition, the contact structures are relatively easily deformed when subjected to the closing force applied to the contacts.While the deformation of the contact structures resulting from repeated closings will work harden the structures, the reusltant deformation of the contact structures is most undesirable.

Thus, it has been found highly desirable, particularly in the case of cup-type contacts, to provide a means for strengthening the contact structure, particularly when the walls thereof are weakened by providing slots to cause rotation of the arc on the contact surfaces.

Summary of the invention In accordance with the present invention, a contact structure for a vacuum circuit breaker is provided wherein a cup-shaped contact structure including arc rotation slots, is strengthened by incorporating a reinforcing means. The contact structure includes a principal memberformed of a material of high electrical conductivity such as copper or copper alloy and a ring-shaped contact member which is also preferably formed of copper or of a copper alloy. The principal member comprises three portions, a support portion, a mid-portion, and a closed wall portion extending from the mid-portion in the opposite direction from the support portion. The enclosed wall portion forms with the mid-portion a cupshaped structure, upon the lip of which is mounted the ring-shaped contact member.The ring-shaped contact member is secured to the rim of the cup-shaped structure by a brazing operation. While the ring-shaped contact member is continuous, that is without grooves, rotation of the arc is brought about by providing helical grooves in the closed wall portion. In orderto prevent deformation ofthe contact structure, and more particularly of the closed wall portion thereof, a reinforcing means is provided, which extends between the mid-portion of the contact structure and the ring-shaped contact member. In one embodiment, this reinforcing means, which is formed of a material of high strength and higher electrical resistivity than said copper, is supported at one end by the mid-portion of the contact structure and engages and supports the ring-shaped contact member at the opposite end.

With the closed walled portion portion formed as a circular cylinder, the reinforcing member is also formed as a circular cylinder which fits within the closed wall portion. The contact ring covering the free ends of both the closed wall portion and the reinforcing member. In another embodiment of the invention, the closed wall portion may be formed with a circular cylindrical outer wall and a truncated conical inner surface. In this embodiment the rein- forcing means is in the form of a hollow truncated cone, the outer surface of which engages the inner truncated conical surface of the closed wall portion.

Brief description of the drawings In order that the invention may be clearly understood and readily carried into effect, contactstructures for a vacuum circuit interrupter in accordance therewith will now be describe, by way of example, with reference to the accompanying drawing in which: Figure lisa side view of a pair of vacuum circuit interrupter contact structures in accordance with one embodiment of the invention.

Figure 2 is a cross-sectional view of the contact structure shown in Figure 1.

Figure 3 is a cross-sectional view of a vacuum circuit interrupter contact structure in accordance with a second embodiment of the invention.

Description of the preferred embodiments While this invention is susceptible of embodiments in many different forms, there is shown in the drawings, and will herein be described in detail, two preferredembodiments of the invention. It should be understood, however, that the present disclosure is to be considered as exemplification of the principles of the invention, and is not intended to limit the invention to the specific embodiments illustrated.

Turning to the drawing, Figure 1 illustrates a pair of contact structures 10 and 12 constructed in accordance with a first embodiment of this invention. The same first embodiment of this invention is shown in cross-section in Figure 2. Each of the contact structures includes a first member 14 which comprises a support portion 16, a mid-portion 18 and a closed wall portion 20. In the preferred embodiment, the first emmber 10 is formed as unitary structure from copper or copper alloy.

The support portion 16 is showned formed as a cylindrical member, the ends of whih are broken away, so as to suggest that they may be of any desired length. The support portion 16 provides a means whereby electrical and mechanical connections may be made to the contacts for the purpose of conducting electrical current from the contact and for connecting the contacts to the vacuum interrupter housing and the contact operating mechanism.

The mid-portion 18 is shown to be of a solid cylindrical form with a greater diameter than the support portion 16. The closed wall portion 20 is shown to be a hollow circular cylindrical member, the outside diameter of whih corresponds to that of the adjoining mid-portion 18. A cylindrical aperture 22 is formed by the inside surface 24 of the closed wall portion 20, and a circular base 26 provided by the mid-portion 18.

In accordance with this invention, a reinforcing means 28, in the form of a hollow circular cylinder, is provided within the cylindrical aperture 22. The reinforcing means or circular cylinder 28 is formed of a non-magnetic material which will retain its strength when subjected to the high temperatures incurred during a brazing cycle, which is a portion of the assembly procedure for a vacuum interrupter utilizing the contacts of this invention. The preferred material, which meets these requirements, is A.l.S.I.

304 Stainles Steel. Other non-magnetic metals which are suitable for use in forming the reinforcing member are tungsten, titanium, zirconium, and molybdenum, i.e., metals from groups 1VB, VB, and V1B of the periodic table, and beryllium oxide, high density aluminium oxide, and boron nitride.

As shown in Figures 1 and 2, the outside surface of the reinforcing means 28 abuts the inside surface 24 of the closed wall portion 20. A ring-shaped contact 30 is secured to the exposed ends of the closed wall 20 and reinforcing means 28. The inside diameter 32 of the ring-shaped contact 30 corresponds to the inside diameter ofthe reinforcing means 28, while the outside diameter 34 of the ring-shaped contact corresponds to the outside diameter of the closed wall 20. Thus, since the ring-shaped contact 30 completely covers the ends of the reinforcing means 28 and the closed wall 20, any arc established between the ring-shaped contacts 30 will be prevented from terminating on the reinforcing means 28 or the closed wall 20.

In an elongated contact thus assembled, the reinforcing means or cylinder 28 supports the ringshaped contact 30 from the mid-portion 18, thus preventing deformation ofthe closed wall portion 20 when the mating ring-shaped contacts 30 engage each other in a circuit closing operation. In a preferred manner of assembling the elongated vacuum interrupter contact structure of this invention, the ring-shaped contact 30 is secured to the principal contact structure 10 buy a brazing operation.

The reinforcing means 28 is secured in the same operation.

While the reinforcing cylinder 28 is shown in Figures 1 and 2, as a solid member, it need not be so formed. For instance, it could also be formed as a pair of rings, one engaging the ring-shaped contact 30 and the other engaging the mid-portion 18, with a plurality of spots or rods maintaining the rings in a predetermined spaced position.

The need for the rinforcing means 28 is particularly great when slots 36, such as are shown in Figure 1, are provided in the closed wall 20 for the purposes of enhancing the rotation of the arc around the surface of the ring-shaped contact 30. The provision of the slots 36 considerably weakens the closed wall portion 20 such that without the reinforcing cylinder 28, the engagement of the contact rings 30 during a contact closing operation would more likely deform the closed wall portion 20.

If the reinforcing cylinder 28 is a solid member, when slot 36 are provided in the closed wall 20, apertures or slots may also be provided in the reinforcing cylinder 28, in alignment with the slots 36, in order to vent the volume formed within a pair of the cup-shaped contacts when they are closed.

A second embodiment of this invention is shown in Figure 3. Those elements of Figure 3 which correspond to those in Figures 1 and 2, without material change, are identified by the same numerals as the corresponding elements in Figures 1 and 2.

The embodiment shown in Figure 3 differs from that shown in Figures 1 and 2, in that the reinforcing member 40 is formed as a hollow truncated conical member rather than as a hollow right circular cylindrical member. Inside surface 42 of the closed wall portion 20 is also formed as a truncated conical surface, such that upon assembly, it will engage the outer surface of the reinforcing member 40. As in the case of the previous embodiment, one end of the reinforcing member 40 engages the mid-portion 18 at the base 26, while the other end engages the under surface of the ring-shaped contact 30 to support it from the mid-portion 18.

While in the preferred embodiments the principal contact structues 10 and 12 are formed of copper or a copper alloy, the ring-shaped contact 30 is also formed of a copper alloy, and the reinforcing member is formed of stainless steel (A.l.S.l. 304 Stainless), other materials could also be used. For instance, it would appearthatthe reinforcing means which should be formed of a material which retain its strength following a high temperature brazing cycle and which should be non-magnetic, could be formed of other materials as previously set forth.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of this invention. For example, although two specific embodiments have been illustrated and described in detail, the reinforcing means of this invention could be embodied in other physical configurations. for instance, the outside diameter of the closed wall portion 20 could be less than that of the mid-portion 18, such that a ledge would be formed on the mid-portion 18 which could support a reinforcing means surrounding the outer periphery of the closed wall portion 20. It is further envisioned that an annular slot could be formed within the closed wall 20, such that the base of the slot could be formed by the mid-portion 18, whereupon a reinforcing member placed within the slot would engage and support the lower surface of the ring-shaped contact 30. It should be understood that no limitations with respect to the embodiments illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope thereof.

Claims

CLAIMS What is claimed is as follows:

1. An elongated contact structure suitable for use in avacuum circuit breaker comprising: a) A mid-portion formed of a material of high electrical conductivity, b) A support portion, also formed of a material of high electrical conductivity, extending from said mid-portion in a first direction generally along the longitudinal axis of the elongated contact structure, c) A closed wall portion, also formed of a material of high electrical conductivity, extending from said mid-portion in a second direction, opposite said first direction, generally along the longitudinal axis of the elongated contact structure, said wall portion extending from said mid-portion so as to form with said mid-portion a cup shaped structure, d) A ring-shaped contact member supported on the free end of said wall portion, said ring-shaped contact member having a radial thickness in the direction perpendicular to the longitudinal axis, which is greater than that of the free end of said closed wall portion, said ring-shaped contact member having a contact engaging surface facing in the second direction, and a support surface facing in the first direction, said support surface having first and second portions, said first portion of said support surface engaging the free end of said closed wall portion to form an electrical connection therebetween, e) A reinforcing means formed of a material of higher electrical resistivity than said wall portion extending between said mid-portion and said second portion of said support surface of said ring-shaped contact member to support said ringshaped contact member from said mid-portion, thereby preventing deformation of said wall portion when a closing force is applied to said ring-shaped contact memberthrough engagement of another contact structure with said contact engaging surface.

2. The elongated contact structure of claim 1, wherein said material of higher electrical resistivity is a non-magnetic material.

3. The elongated contact structure of claim 1, wherein said material of high electrical conductivity is copper or copper alloy, and said material of higher electrical resistivity is stainless steel.

4. The elongated contact structure of claim 1, wherein said closed wall portion is formed as a circular cylinder, said ring-shaped contact member is formed as a circular disk, and said reinforcing means is formed as a circular cylinder.

5. The elongated contact structure of claim 4, wherein the outside diameter of said closed wall portion ring-shaped contact member, the inside diameter of said closed wall portion is essentially the same as the outside diameter of said reinforcing means is essentially the same as the inside diameter of said ring-sahped contact member.

6. The elongated contact structure of claim 5, wherein said material of higher electrical resistivity is a non-magnetic material.

7. The elongated contact structure of claim 5, wherein said material of high electrical conductivity is copper or copper alloy, and said material of higher electrical resistivity is stainless steel.

8. The elongated contact structure of claim 1, wherein a plurality of slots are formed in said closed wall portion extending completely through the radial thickness of said closed wall portion, said slots extending from the free end of said wall portion toward said support portion, and being inclined with respect to the longitudinal axis of the elongated contact structure.

9. The elongated contact structure of claim 8, wherein said closed wall portion is formed as a circular cylinder, said ring-shaped contact member is formed as a circular disk, and said reinforcing means is formed as a circular cylinder.

10. The elongated contact structure of claim 9, wherein at least one aperture is provided in said reinforcing means in communication with at least one of said slots, whereby the volume formed within said cup-shaped structures when a pair of said contact engaging surfaces are engaged with each other, is vented.

11. The elongated contact structure of claim 9, wherein the outside diameter of said closed wall portion is essentially the same as the outside diameter of ring-shaped contact member, the inside diameter of said closed wall portion is essentially the same as the outside diameter of said reinforcing means, and the inside diameter of said reinforcing means is essentially the same as the inside diameter of said ring-shaped contact member.

12. The elongated contact structure of claim 11, wherein said material of high electrical conductivity is copper or copper alloy, and said material of higher electrical resistivity is stainless steel.

13. The elongated contact structure of claim 1, wherein said closed wall portion is formed with an outer circular cylindrical surface and an innertruncated conical surface having a greater diameter at the free end than adjacent said mid-portion, and said reinforcing means being formed as a hollow truncated cone, the outer surface of which engages said inner truncated conical surface of said closed wall portion.

14. The elongated contact structure of claim 13, wherein said material of high electrical conductivity is copper or copper alloy, and said material of higher electrical resistivity is stainless steel.

15. The elongated contact structure of claim 13, wherein a plurality of slots are formed in said closed wall portion extending completely through the radial thickness of said closed wall portion, said slots extending from the free end of said wall portion toward said support portion, and being inclined with respect to the longitudinal axis of the elongated contact structure.

16. The elongated contact structure of claim 15, wherein at least one aperture is provided in said reinforcing means in communication with at least one of said slots, whereby the volume formed within said cup-shaped structures when a pair of said contact engaging surfaces are engaged with each other, is vented.

17. An elongated contact structure substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 os the accompanying drawings.