GB2061010A

GB2061010A - Vacuum type circuit interrupter

Info

Publication number: GB2061010A
Application number: GB8032211A
Authority: GB
Original assignee: Gemvac KK; Meidensha Corp; Meidensha Electric Manufacturing Co Ltd
Current assignee: Gemvac KK; Meidensha Corp; Meidensha Electric Manufacturing Co Ltd
Priority date: 1979-10-09
Filing date: 1980-10-07
Publication date: 1981-05-07
Also published as: DE3037752C2; JPS6129151Y2; JPS5657444U; DE3037752A1; GB2061010B

Abstract

A vacuum type circuit interrupter comprising a contact electrode 14 of substance, having a high electrical conductivity, containing an additive of high vapour pressure in a proportion such that the contact electrode cannot be brazed to other component, and a cup- shaped supporting member 19 of high electrical conductivity, brazed to an electrode 13 on the the end face of a contact rod 3, and in which the contact electrode 14 is fitted into the supporting member 19 and then fixed thereto by deformed extensions 20 of the cup- shaped member 19 engaging in an annular groove 21. <IMAGE>

Description

SPECIFICATION Vacuum type circuit interrupter The present invention relates to vacuum type circuit interrupters.

In the prior art, in order to eliminate surges occurring when opening and closing a vacuum type circuit interrupter, specifically, a surge accompanied by an electric current chopping phenomenon at the time of interruption of a small electric current, an attempt has been made to reduce the chopping current level by the use of contacts of silver-tungsten carbide material which will be called "Ag-WC system" hereinafter or of a copper-bismuth material which will be called "Cu-Bi" hereinafter.

In the Ag-WC system, contact electrodes incorporating tungsten carbide whose specific electrical resistance is high become heated in the neighbourhood of arc spots. This heating results in the vaporisation of part at least of the content of the contact electrode thereby prolonging the arc about the time of a natural zero in the electric current. In the Cu-Bi system, bismuth having a low melting point and with a high vapour pressure is vaporised due to the heating in the vicinity of arc spots.

However, when using the Ag-WC system to interrupt a large electric current, it is found that the arc spot is stationary with respect to the electrical surface of the contact as understood from a chopping characteristic, that is the value of the chopping electric current is high.

Accordingly, it has been proposed to disperse the arc spot and thereby prevent it from adopting a fixed position on an electrical contact by using the socalled "axial magnetic field" taught, for instance, in U.S. Patent Specification No. 3,283,103 - Allan et al.

As will be appreciated from the above discussion, there have been problems in the respective interrupting characteristics at the time of interruption of small and large current.

With the above in mind, an object of the present invention is to provide a vacuum type circuit interrupter which makes it possible to maintain a chopping current flowing through a contact electrode, and thereby reduce the value of chopping surges at the time of the interruption of a small current.

According to the present invention, a vacuum type circuit interrupter comprising a pair of contact rods disposed so as to be in contact with each other or away therefrom within a vacuum vessel, and a disk-shaped contact electrode attached to the axial ends of each of contact rods, respectively, is characterised in that each of contact electrodes is provided on the outer circumferential surface thereof with an annular groove, each contact electrode made of substance having a high electrical conductivity and containing an additive of high vapour pressure substance in such a proportion that the contact electrode cannot be brazed to another component, and that the vacuum power interrupter further comprises a cup-shaped supporting member, having a high electrical conductivity, brazed to the axial end of the contact electrode, the supporting member having an annular flange provided along the outer periphery thereof, whereby each contact electrode is fitted into the supporting member and then fixed thereto in such a manner that the edge of the annular flange of the supporting member is fitted into the annular groove of the contact electrode with a caulking method.

By way of example only, vacuum type interrupters embodying the present invention will now be described in more detail with reference to the accompanying drawings in which: Figure 1 is a side view partly in section of a vacuum type circuit interrupter embodying the present invention, Figure 2 is a cross section of part of an arc-shield member supporting structure included in the embo dimentshown in Figure 1, Figure 3 is a perspective view of the arc-shield member, Figure 4 is a plan view of a movable electrical contact, Figure 5is a cross section along the line V-V of Figure 4, and Figure 6 is a side view partly in section of an alternative form of movable electrical contact.

In the drawings, the same reference numerals denote corresponding or similar parts of a vacuum type circuit interrupter embodying the present invention.

Figure lisa side view partly in section of a vacuum type circuit interrupter embodying the present invention. The interrupter comprises a vacuum vessel 1 which is evacuated to high degree of vacuum, and stationary and movable contact rods 2 and 3 respectively oppositely disposed within the vacuum vessel 1 as shown. Electrical contacts 4 and 5 are attached respectively to the axial ends of the stationary and movable contact rods 2 and 3, and a cylindrical, metallic, arc-shield member 6 is concentrically disposed around the stationary and movable contacts 4 and 5 within the vacuum vessel 1. An actuating unit (not shown) is connected to the outwardly-extending end of the movable contact rod 3.

In more detail, the vacuum vessel 1 includes annular flanges 8 one end of each of which is embedded in the adjacent end of a cylindrical insulating envelope 7 of glass, the other ends of tubular flanges 8 being joined to end plates 9 as shown.

The stationary contact rod 2, of high electrical conductivity material, for example Cu, is inserted into a hole formed in one end plate 9 serving as a cover plate for the vacuum vessel 1 and is hermetically fixed therein. The movable contact rod 3, also of a material of high electrical conductivity, for example Cu, is inserted into a hole formed in the other end plate 9 serving as a bottom plate of the vacuum vessel so as to be movable in the axial direction and is hermetically sealed to one end of a bellows unit 10 whose other end is hermetically sealed to the adjacent end plate 9.

As previously mentioned, the movable contact rod 3 is connected at the outwardly extending end thereof to the actuating unit for actuating the movable contact rod 3 in an axial direction towards and away from the fixed rod 2to bring the electrodes 4, 5 into contact and to separate them.

A plurality of supporting members 11 for supporting shield supporting members to be described below is embedded in the vicinity of the middle portion in the longitudinal direction of the insulating envelope 7 and spaced at predetermined intervals around the circumference of the envelope 7. Each of the supporting members 11, as best shown in Figure 2, comprises a cylindrical fitting portion 1 lea projecting from the inner peripheral surface of the insulating envelope 7, a conical portion 11 b integral with the fitting portion 1 1a, and a turned-over portion 1 1c formed at the end of the conical portion 1 1h and extending generally coaxially with the fitting portion 11 a.The conical portion 11 b and the turned-over portion 1 1c are embedded in the insulating glass envelope 7 by heating, thereby enlarging the contact area to ensure secure fixing.

As best shown in Figures 2 and 3, each of the arc-shield supporting members 12 is of a length approximately the same as the axial length of the metallic arc-shield 6 and has a middle portion which is bent to be dog-legged shaped. Each member 12 is supported on one of the members 11 'by mounting a cylindrical fitting portion 1 2a on the member 12 over the fitting portion 11 a of the member 11.

The arc-shield supporting member 12 is further provided at each end with a portion 1 2b of arcuate shape by means of which the arc-shield member 6 is fitted to both ends supported with its axis concentrically disposed within the insulating envelope 7. As can be seen, the shield 6 surrounds part of the length of the stationary and movable contact rods 2,3 and the stationary and movable contacts 4, 5. The shield is fixed to the portion 1 2b by welding. Accordingly, the electric potential of the metallic arc-shield 6 "floats" because the metallic arc-shield 6 is supported by the insulating envelope 7 via the supporting members 11 and the arc-shield supporting members 12.

The movable electric contact 5 comprises a magnetic driving electrode 13 of disc-like form whose outer radius is greater than that of the movable contact rod 3, and a button-shaped contact electrode 14. In more detail, the magnetic driving electrode 13 of high electrical conductivity material, for example Cu or Ag is fastened to the end face of the movable contact rod 3 by fitting the end of the movable contact rod 3 into an annular recess 15 provided in the central portion of the bottom surface of the electrode 13, the parts then being fixed together by brazing.

There is formed a plurality of slits 16 on the magnetic driving type electrode 13 inclined at predetermined angles with respectto both the radial and axial directions of the disc. Thus, there are formed a plurality of screw-shaped, arc-driving sectors 17 by extending the slits 16 in the vicinity of the outer periphery of the recess 15. Over the central portion of the upper end surface of the magnetic driving electrode 13, there is provided an annular recess 18 of which radius is greater than that of a circle defined by the inner lower portions 16a of the slits 16. A cup-shaped supporting member 19 of high electrical conductivity material, for example Cu or Ag which is softened by annealing after the supporting member 19 is joined to the electrode 13 by brazing is fitted into the recess 18 and fixed thereto by brazing.There is formed a plurality of wave-shaped portions or serrations 19a on the inner bottom portion of the supporting member 19. The height of a flange 19b provided along the outer periphery of member 19 is approximately the same as the depth of the recess 18. There is a plurality of spaced projections 20 on the flange 196 which are forced into a groove 21 by caulking as will be described below. The projections 20 are positioned in the circumferential direction at spaced, predetermined circumferential intervals.

The contact electrode 14 is so mounted on the supporting member 19 that the wave-shaped portion 14a formed in the bottom surface of the electrode engages the wave-shaped portion 19a of member 19.

The contact electrode 14 is made of material of medium vapour pressure and high electrical conductivity, for example Cu or Ag and containing in an amount of from 10 to 20% by weight of substance of low melting point and high vapour pressure, for example bismuth or antimony. The amount is such that the electrode cannot be brazed, in order to maintain the level of chopping electric current to be 0.5A to 1A. The contact surface (corresponding to an upper surface in Figure 5) of the electrode 14 projects from the adjacent surface of the magnetic driving electrode 13 buy a predetermined distance. An annular groove 21 is formed around the outer periphery of electrode 14 as shown. The projections 20 of the supporting member 19 are fitted into the groove 21 by caulking.The contact electrode 14 is further provided with a circumferential recess 14b on the central portion of the contact surface of the electrode 14. Thus, the whole appearance of the contact electrode 14 resembles that of a button.

Reference is made to the caulking of the upper end of the projection 20 of the supporting member 19. As shown by a broken line in Figure 5, the caulking is effected by pressing the contact electrode 14 into the supporting member 19 with-a pressing tool 22, inserting a fork-shaped tool 23 with a caulking portion 23a and a reinforced portion 23b between the pressing member 22 and the arc driving sectors 17 and caulking the projections 20 into the groove 21. Thus, the electrode is securely fixed to the contact.

The above description is of the movable electrical contact only and the fixing thereof to the movable contact rod 3. However, the stationary electrical contact 4 is of a generally similar construction and the components are secured together in like manner.

The stationary electrical contact 4 is of the same form as the movable electrical contact 5 with the exception that the slit 16 of the magnetic driving type electrode 13 is so formed that the path of an arc current is of] or channel shape. Accordingly, the same reference numerals are attached to the corresponding constituent members of the fixed electrical contact 4 having the same function as that of the movable electrical contact 5, and fixed contact will not be further described.

Alth-ough the aforementioned embodiment has magnetic driving electrical contacts of a screw type, the same result can be obtained with the more usual spiral electrical contacts.

Reference numerals 24 in Figures 1 and 5 denote a cup-shaped axial arc-shield member for protecting the stationary contact rod 2 and the bellows 10.

The vacuum type circuit interrupter just described is made by a method including the following: When attaching the contact electrode containing the addition substance having low melting point and of high vapour pressure in a proportion such that the electrode cannot be brazed to the magnetic driving electrode, the cup-shaped supporting member which is made of high electrical conductivity material and softened by a brazing temperature at that time is used. Further, the supporting member is joined to the magnetic driving electrical contact.

With such a construction, the vacuum type circuit interrupter embodying the present invention makes it possible to improve the strength of the arc driving sectors of the magnetic driving electrode whose mechanical strength is otherwise low and to facilitate the fastening of contact electrode to the magnetic driving electrode by securing the projections of the supporting member into the groove of the contact electrode by caulking since brazing is impossible.

Further, a feature of electrode structure resides in the combination of the contact electrode containing the above mentioned electrode material therein and the screw-shaped magnetic driving type electrode.

Accordingly, this makes it possible to maintain the level of a chopping current at a value of from 0.5A to 1A, thereby reducing the chopping surge at the time of the interruption of a small current. Further, this ensures that an arc seated on the contact electrodes can be moved outwardly and rotated by a magnetic driving electrode to improve the interrupting characteristic of a large current.

Reference is now made to experimental data obtained with an electrical contact structure consisting of the disk-shaped contact electrode or solely of the button-shaped contact electrode or the screwshaped magnetic driving electrode: 1) When using only a disk-shaped contact electrode containing Cu, as main material, including 10% by weight of Bi and having an outer radius of 40mm, the value of the chopping electric current is 1A, permitting the interruption of currents up to 1 OKA.

2) When using the combination of a buttonshaped contact electrode containing Cu, as a main material, including 10% by weight of Bi and a screw electrode of Cu having an outer radius of 40mm, the value of the chopping electric current is 1A, permitting the interruption of currents of from 20 to 25KA.

3) When using only a disk-shaped contact electrode containing a Cu, as a main material, including 20% by weight of Bi, the value of the chopping electric current is 0.5A, permitting the interruption of currents up to 1OKA.

4) When using the combination of a contact electrode containing Cu as a main material and including 20% by weight of Bi and a screw electrode of Cu having an outer radius of 40mm, the value of the chopping electric current is 0.5A, permitting the interruption of currents of from 16 to 20KA.

Figure 6 shows a stationary electrode 5' of the axial magnetic field electrode structure.

The stationary electrode 5' comprises an electrode 25 of annular form for producing a magnetic field in parallel with the axis of the movable contact rod 3, that is, an axial magnetic field, and an umbrellashaped contact electrode 26. The electrode 25 comprising a ring-shaped portion 25a of which the radius is greater than that of the movable contact rod 3, and a disk-shaped mounting portion 25b located in the central portion of the portion 25a. One end of portion 25b has a central recess 27 from which extends a radial arm (not shown) whose outer end is secured to the portion 25a by brazing. In the other end surface of the mounting portion 25b, is a central disk-shaped recess 28.A supporting member 29 comprising a material having a high electrical resistance, for example stainless steel, projects upwardly from the mounting portion 25b and is secured in the recess 28 by brazing.

On the end of the supporting member 29, a cup-shaped member 30 of high electrical conductivity material, for example Cu or Ag which is softened by means of annealing due to the brazing temperature after the member 30 is joined to the member 29 with brazing, is integrally mounted. The outer radius of the supporting member 30 is approximately the same as that of the coil electrode 25. At the end edge of the flange of the supporting member 29, there are provided a plurality of projections 31 so as to position at a predetermined interval in the circumferential direction.

The contact electrode 26 having an outer radius of the same value as the inner radius of the supporting member 30 is fitted into the supporting member. The contact electrode 26 disposed so that it becomes contact with each other or away therefrom. The contact electrode 26 has a main constituent of a high electrical conductivity and of medium vapour pressure, for example Cu orAg containing an additive, for example bismuth or antimony having a low melting point and of a high vapour pressure material in an amount by weight of from 10 to 20% and in such a proportion that the electrode 26 cannot be brazed.

The contact electrode 26 is provided at the contact surface with a contact portion 26a and a bevelled edge portion 26b. The contact electrode 26 is further provided at the outer circumferential surface thereof with an annular groove 32 for receiving a circumferential projection 31 on the supporting member 30, the projection being secured in the groove by caulking. The contact electrode 26 is easily fixed to the supporting member 30 by securing the projection 31 into the groove 32 by caulking after the contact electrode 26 is engaged with the supporting member 30.

The component designated by reference numeral 33 in Figure 6 is a connecting conductor for connecting the other end of the portion 25a of the electrode 25 with the contact electrode 26. Reference numeral 34 denotes an electrode reinforcing member made of a material having a high electrical electric resistance, for example stainless steel fitted into the movable contact rod 3. The above description is of a movable electrode 5', bust a description of the co-operating stationary electrode (not shown) will be omitted because the construction of the stationary electrode is substantially the same as that of the movable electrode.

Accordingly, the electrode structure just described makes it possible to reduce the chopping surge by suppressing the chopping current level, at the time of the interruption of a small current, to a value within the range of from 0.5A to 1A. The electrode structure further makes it possible to disperse the arc produced between contact electrodes by the axial magnetic field due to the coil electrode and thereby improve the interrupting characteristics of a large current. Furthermore, the electrode structure facilitates the mounting, with respect to the contact rod, of the contact electrode to which the rod cannot be brazed.

Claims

1. A vacuum type circuit interrupter comprising a pair of contact rods relatively movable towards and away from each other within a vacuum vessel, and disc-shaped contact electrodes attached to the axial end faces of the contact rods, in which each contact electrode has in its outer circumferential surface an annular groove, and is made of a material having a high electrical conductivity and containing an additive of high vapour pressure that is present in a proportion such that the contact electrode cannot be brazed to another component, in which the interrupter further comprises a cup-shaped supporting member, having a high electrical conductivity, brazed to the axial end face of the contact electrode, said supporting member having an annu larflange on the outer periphery thereof, and in which each contact electrode is fitted into said supporting member and then fixed thereto in such a manner that the edge of the annular flange of said supporting member is secured in the annular groove of said contact electrode by caulking.

2. An interrupter as claimed in claim 1, wherein said contact electrode is made of a material selected from the group comprising copper and silver and in which the additive is selected from the group comprising bismuth and antimony.

3. An interruption as claimed in claim 2 in which the weight of the additive is from 10 to 20% of the total weight of the material.

4. An interruption substantially as herein described with reference to and illustrated by Figures 1-5 or Figure 6 of the accompanying drawings.