GB2236429A

GB2236429A - Conditioning components

Info

Publication number: GB2236429A
Application number: GB9020735A
Authority: GB
Inventors: John Ernest Jenkins
Original assignee: GEC Alsthom Ltd
Current assignee: Alstom UK Ltd
Priority date: 1989-09-22
Filing date: 1990-09-24
Publication date: 1991-04-03
Also published as: WO1991004567A1; ZA907603B; GB8921475D0; GB9020735D0

Abstract

A vacuum switch contact conditioning process whereby switch contacts are conditioned before assembly in the switch. The contacts are mounted in a vacuum chamber and subjected to an electron beam or laser which is scanned over the contact surface to heat and melt it locally. The contact is thus degassed and metallurgically re-structured to provide durability.

Description

High Current Switch Components This invention relates to high-current-switch components and in particular to a method of conditioning such components prior to operation of the switch.

Before switches with a high interrupting capacity are put into operation, the contacts of the switch are commonly conditioned to improve the breaking capacity and dielectric performance. This process can be carried out by using the switch to interrupt half cycle 'loops' of current of increasing magnitude until some specified current, usually greater than the switch will see in service, is reached. For each current magnitude the polarity must be reversed so that each contact is subjected to similar arcing conditions.

The apparatus required to condition a switch in this manner is complex, usually consisting of a large capacitor bank together with an actuator for opening and closing the switch, timing electronics, and recording apparatus to check how the switch has performed. The process is slow and not suitable for large batches of switches. In view of these difficulties an alternative method of conditioning the switch components is to be desired.

During conditioning in the above manner the contact surface rapidly melts to a depth of the order of 10 microns as the cathode spots move over it, allowing the absorbed gases in the surface layer to be released. The surface layer then rapidly resolidifies thus altering the physical and metallurgical properties of this layer. This conditioning process is a very efficient form of vacuum degassing together with a surface modification effect caused by the rapid melting and resolidification.

An object of the present invention is therefore to achieve comparable conditioning of switch contacts and other components while avoiding some of the difficulties of the known method.

According to one aspect of the present invention, in a method of conditioning a switch component which in operation is subject to a heating effect resulting directly or indirectly from high-current arcs, the component, separate from any switch body, is positioned in a vacuum chamber and is heated by an energy beam to a temperature in excess of the maximum working temperature of the component in operation.

The component is preferably heated to a temperature such as to cause local melting of the component surface.

The energy beam may be an electron beam or a laser beam and may be scanned over the surface of the component.

The component may be a switch contact.

A plurality of switch contacts may be mounted in the vacuum chamber and then scanned by the beam in a single operation.

According to another aspect, the invention comprises a high-current switch manufactured in such manner as to include a method as aforesaid.

According to a further aspect of the invention, in a method of conditioning a metal surface which in subsequent operation is to be subject to local heating such as to produce local melting or near melting, the metal surface, without the addition of any added material, is heated in a vacuum chamber by an energy beam scanned over the surface to a temperature locally in excess of the maximum operating temperature.

A method of conditioning high-current switch components in accordance with the present invention will now be described, by way of example.

A high-current switch such as a vacuum contactor may have to operate on currents of thousands of amps. Arc currents of this magnitude can cause considerable damage to a switch contact with the resultant emission of gases and vapourised contact material. Pre-conditioning of the contact to de-gas it, improve its metallurgical and thermal properties and generally stabilise its operation, is therefore highly desirable.

In accordance with the invention, a number of contacts, with or without their supporting conductors, are mounted in a line or array in a vacuum chamber. An electron beam gun is directed at the contacts, the beam being focussed to a fine spot and driven to scan the whole of each contact surface and then to move on to the next. The operating surface is thus heated to a temperature rather greater than the maximum operating temperature, and preferably sufficient to melt the surface locally. The spot size, power and scanning speed are chosen preferably to give the same depth of melting as that obtained with arc conditioning. Clearly, of course, the energy level is maintained below a level that would produce permanent distortion of the surface contour. Energisation of the electron beam is controlled in synchronism with the scan so that it is 'on' only when directed at a contact surface.

Once conditioned in this way, the contacts are mounted in the envelope of the vacuum switch and the envelope evacuated and sealed.

A large number of contacts can be automatically processed and then built into switches with the additional advantage of not producing the spatter on the inside of the switch that is normally produced by arc conditioning.

After the switch is built, some processing, by low current arcing or high voltage flashing, might still be necessary to remove the absorbed surface layer of gas acquired during building.

While the invention is primarily directed to the preconditioning of switch contacts it can also be applied to other switch components that are, in operation, heated directly or indirectly by the arc. Spatter shields for example, employed to protect the vacuum envelope insulator, are subjected to heating by spattered molten metal and vapour in the presence of an arc.

A laser beam, pulsed or C.W., may be employed instead of the electron beam.

The process is also applicable to the pre-conditioning of metal surfaces generally which are, in subsequent operation, subject to high temperatures such as to cause local melting or near melting.

Pre-conditioning according to the present method is independent of any material additive such as may be used in surface hardening techniques.

The application to high current switch components remains, however, the one giving the most outstanding improvement over the long established prior art method.

Claims

1. A method of conditioning a switch component which in operation is subject to a heating effect resulting directly or indirectly from high-current arcs, in which method the component, separate from any switch body, is positioned In a vacuum chamber and is heated by an energy beam to a temperature in excess of the maximum working temperature of the component in operation.

2. A method according to Claim 1 wherein said component is heated to a temperature such as to cause local melting of the component surface.

3. A method according to Claim 1 or Claim 2, wherein said energy beam is an electron beam or a laser beam.

4. A method according to any preceding claim, wherein said energy beam is scanned over the surface of the component.

5. A method according to any preceding claim, wherein said component is a switch contact.

6. A method according to Claim 5, wherein a plurality of switch contacts are mounted in said vacuum chamber and are scanned by said beam in a single operation.

7. A method according to any of Claims 1, 2, 3 and 4, wherein said component is a spatter shield.

8. A method of conditioning a switch contact substantially as hereinbefore described.

9. A method of conditioning a metal surface which in subsequent operation is to be subject to local heating such as to produce local melting or near melting, in which method the metal surface, without the addition of any added material, is heated in a vacuum chamber by an energy beam scanned over said surface to a temperature locally in excess of the maximum operating temperature.

10. A high-current switch manufactured in such manner as to include a method according to any preceding claim.