GB2105910A - A contact member for vacuum isolating switches - Google Patents

Abstract

A contact member, particularly in the form of a rod or bolt, for a vacuum isolating switch, consists, at least in the contact zone, of copper, 15% by weight of aluminium and 0.1 to 10% by weight of one or more of the elements Bi, Te, Se, Sb, Mg, and additionally cobalt. In this way the switching capacity of the contact is increased as compared with contacts made of known alloys containing nickel and burning-off is reduced. The alloy may be produced in a particularly simple manner by applying the further constituents (4) which are to be alloyed into the copper, to the end of a copper rod or bolt (1) in solid form and subsequently heating them above the melting point of at least some of the constituents, to effect formation of the required alloy. The contact members of the invention are particularly suitable for use in load isolating switches in medium-voltage switching arrangements. <IMAGE>

Description

SPECIFICATION A contact member for vacuum isolating switches The present invention relates to a contact member, particularly in the form of a rod or bolt, for a vacuum isolating switch.

In German Patent Specification No.

2,723,822, as open to inspection, there is described a contact member for use in a vacuum isolating switch, which on operation of the switch moves into contact with a counter-contact member, the contact member, at least in the region of contact, being made of an alloy comprising copper, aluminium and at least one element Me selected from bismuth, tellurium, selenium, antimony and magnesium, the aluminium content of the alloy being at least 15% by weight, and the total content of the element or elements Me being between 0.1 and 10% by weight.

In medium voltage switching arrangements, for example, vacuum isolating switches have to switch on and off the operating current, to switch on the impedance making current and to hold the rated flash-over surge voltage and the rated alternating voltage when in the open position; however, they do not have to control the strength of the impedance breaking current of the switching arrangement. They should, therefore, offer advantages as regards cost, in comparison with power switches.

In another connection, namely for vacuum contact breakers intended to interrupt high curents, German Patent Specification No.

2,922,075 discloses a contact member or bolt, in which high-melting metal powder is accommodated in a copper matrix. Chromium is primarily suggested for use as the highmelting metal therein. In addition to many other metals, including iron, tungsten, molybdenum and iridium, the use of cobalt as the high-melting metal is suggested. These metals serve to reduce the break current, which is necessary to avoid overvoltages.

It is an object of the present invention to provide a contact member for use in vacuum isolating switches with which burning-off is reduced and the life span thereof thus increased.

According to the invention, there is provided a contact member for a vacuum isolating switch, which during operation of the switch, is moved towards an oppositely arranged counter-contact member, said contact member consisting, at least in the contact zone, of an alloy of copper, with less than 15% by weight of aluminium and at least one element selected from bismuth, tellurium. selenium, antimony and magnesium, in a total amount of from 0.1 to 10% by weight, said alloy also containing a proportion of cobalt.

In accordance with the teachings of German Patent Specification No. 2,723,822, nickel is used as an alloying constitutent in a contact member of the general type with which the invention is concerned. However, it has been found that cobalt, which is chemically related to nickel, has considerably more advantageous properties in respect of burning-off and the life span of the contact. This is particularly so, when the contact-making zone of the contact member consists of: 15% to 30% by weight of cobalt; 0. 1% to 5% by weight of an element or elements selected from tellurium, selenium, antimony, magnesium and bismuth; 0.5% to 5% by weight of aluminium; remainder copper.

It is not necessary for the entire contact member to consist of this alloy; it is sufficient if the member essentially consists of copper over a large portion of its length and has a continuous transition as regards its composition into the alloy specified towards the contact-making region. The transition region can be short, relative to the thickness of the contact-making region.

A contact member of this kind can be very advantageously produced by a process in which the alloy constitutents other than copper, are applied in solid form to the end face of a copper contact member in the form of a rod or bolt, the required mixing ratio is adjusted, the alloy constituents are at least partially melted and thus alloyed with one another and with the copper rod or bolt, and if necessary, the required final shape of the contact member is subsequently produced mechanical processing, in particular, by cutting.

The alloy compositions of the present invention allow alloying of the metals with one another and with the copper rod or bolt. It is also possible to produce the contact member by forging.

The alloy constituents are preferably applied in the form of granules of the pure metals or elements. This form allows the mixing ratio to be easily adjusted, thus rendering the process particularly simple.

The heating of the alloy constituents is advantageously carried out abruptly. In this way, a partial evaporation of the more readily volatile elements is largely prevented. The heating operation can advantageously be carried out under high vacuum. An additional protection against the evaporation of relatively easily volatile elements may be provided by heating in an inert atmosphere, in particular of argon.

The heating operation may advantageously be carried out using high-frequency or medium-frequency heating. Gas discharges in argon can thus advantageously be avoided by a low-impedance coupling. Sufficiently abrupt heating can also be effected by means of a furnace having a low time constant.

German Patent Specification No.

1,065,886 discloses a process in which an alloy is separately produced and is then melted onto the end surface of a contat rod or bolt as the finished alloy which already contains the required amount of copper. The alloy described therein is known as a low-melting alloy, whereas in the process in accordance with the invention described above, even high-melting metals, such as the required cobalt, can be incorporated in the alloy. Compared with the process of German Patent Specification No. 1,065,886, the process in accordance with the invention offers a considerable advantage as regards cost, since a separate intermediate alloying of the alloy constituents is not required.

The invention will now be further described with reference to the drawing, which is a schematic side sectional view of the end part of a rod or bolt to illustrate a stage in the production of a contact member according to the invention before the alloying step has been carried out.

A contact rod or bolt 1 consisting essentially of copper is provided in its end face with a recess 2. A mixture 4 of the metals cobalt and aluminium, and at least one element selected from Bi, Te, Se, Sb, Mg, all in granular form, is filled into the recess 2. The mixing ratio of the granular constitutents is so adjusted that it results in the formation of an alloy of the required composition after the alloying of these constitutents with the copper rod or bolt has been effected. The mixture may contain, for example, 75% by weight of cobalt, 12.5% by weight of bismuth, and 12.5% by weight of aluminium. With this mixture, together with the adjacent portion of the copper an alloy of 30% cobalt, 5% bismuth, 5% aluminium and 60% copper is produced, at the end of the rod, after the alloying step.

The total amount of the granular mixture introduced into the recess 2 is advantageously so selected that a smooth surface is produced at the end of the contact member after the formation of the alloy.

Alloying between the constituents of the granular mixture applied to the end of the copper rod or bolt and into the copper bolt is effected to form an edge zone 3 in the rod or bolt 1, which edge zone 3 represents a continuous transition from the alloy formed to the non-alloyed part of the contact rod or bolt 1.

After the heating operation to form the alloy, the surface 5 of the contact rod or bolt is advantageously processed mechanically, in particular being turned or milled off to produce a plane surface. By milling off a relatively thick layer up to a position close to the alloy border region, a fine adjustment of the copper content in the contact-making zone can be achieved.

The alloy used in the contact members of the invention has a favourable welding behaviour during the surge of the making current because of the embrittling element or elements of the group bismuth, tellurium, selenium, antimony, or magnesium, alloyed therein. The presence of cobalt increases the switching capacity and the life span of the contact by reducing burning-off. Even in the alloy, the aluminium present has the property of gettering residual gases during an arc discharge.

The abrupt heating of the contact member to produce the required alloying, can be effected by means of a furnace having a small time constant. High-frequency or medium-frequency heating in an argon atmosphere is also suitable for this purpose. The alloying process is advantageously regulated and monitored by controlling the temperature-time characteristic of the furnace.

The production process in accordance with the invention is generally suitable for alloying copper with tin, lead, magnesium, aluminium, boron, cobalt and iron, with additional admixtures of tellurium or bismuth, which reduce the tendency of the contacts to weld together in the event of a short-circuit. The process is even superior to separately producing the contact material and subsequently soldering it to a copper rod or bolt, because it is considerably cheaper than these processes.

The contact members of the invention are particularly suitable for use in load isolating switches in medium-voltage switching arrangements.

Claims (11)

1. A contact member for a vacuum isolating switch, which during operation of the switch, is moved towards an oppositely arranged counter-contact member, said contact member consisting, at least in the contact zone, of an alloy of copper, with less than 15% by weight of aluminium and at least one element selected from bismuth, tellurium, selenium, antimony and magnesium, in a total amount of from 0.1 to 10% by weight, said alloy also containing a proportion of cobalt.

2. A contact member as claimed in Claim 1, wherein said alloy has the following composition: 1 5 to 30% by weight of cobalt; 0.1 to 5% by weight of one or more of the elements Bi, Te, Se, Sb, and Mg; 0.5 to 5% by weight of aluminium; remainder copper.

3. A contact member as claimed in Claim 1 or Claim 2, in the form of a rod or bolt consisting essentially only of copper over a major part of its length, the composition of the rod or bolt having a continuous transition to a contact zone at one end thereof, consisting of said alloy.

4. A contact member as claimed in Claim 1, substantially as hereinbefore described with reference to and as illustrated in the drawing.

5. A process for producing a contact member as claimed in any one of Claims 1 to 3, comprising the steps of applying the constituents of said alloy other than copper in solid form to one end face of a copper rod or bolt, the mixing ratio of said constitutents being adjusted to produce an alloy of the required composition, alloying said constituents with one another and with the copper rod or bolt by at least partial melting, and, if necessary bringing the contact member to its required final shape by mechanical processing.

6. A process as claimed in Claim 5, wherein the alloy constituents are applied in the form of a mixture of the pure constituents in granular form.

7. A process as claimed in Claim 5 or Claim 6, wherein heating of the alloy constituents is effected abruptly.

8. A process as claimed in any one of Claims 5 to 7, characterised in that the heating step is carried out under high vacuum.

9. A process as claimed in any one of Claims 5 to 7, wherein the heating step is effected in an inert atmosphere.

10. A process as claimed in Claim 9, wherein the inert atmosphere is of argon.

11. A process for producing a contact member for a vacuum isolating switch, substantially as herinbefore described with reference to the drawing.

1 2. A vacuum isolating switch including a contact member as claimed in any one of Claims 1 to 4.