GB2539366A

GB2539366A - Combined spring

Info

Publication number: GB2539366A
Application number: GB1422770.6A
Authority: GB
Inventors: Thomas Falkingham Leslie
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2016-12-21

Abstract

A vacuum switching device comprises a moving electrode that is completely enclosed in an evacuated envelope and mechanically engages and disengages with a fixed electrode to perform a switching function. The moving electrode is connected to an electrically conducting end of the vacuum chamber by an electrically conductive spring component 20 which allows movement of the moving electrode whilst maintaining connection from it to the outside of the device. The spring can provide a closing force, alignment and guidance to a moving electrode and conduct heat away from it to the outside of the device. The spring component can take the form of a helix or a spring washer and be made of a low resistance material such as copper. The spring component may also have a stiffer second spring 25 made of steel to help provide closing forces that can be inside, outside or attached to and interleaved with the first spring (fig 4). The spring may be split into two or more turns (fig 6). The spring connection may be used in a vacuum switch having no external moving parts.

Description

COMBINED SPRING

This invention relates to improvements in vacuum switching devices, which may include for example vacuum interrupters and vacuum switches. The devices are key components within electrical switchgear as used in the transmission and distribution of power. The switchgear may form or be part of a circuit breaker or motor control centre or other installation involving switching.

The general configuration of a vacuum switching device at present is shown in figure I and consists of an evacuated envelope which includes an insulating component I, conducting end plates 2 which enclose a fixed electrode 3 and a moveable electrode 4 that are designed to engage and disengage mechanically to perform the switching function. Normally this movement is permitted without breaking the seal of the evacuated envelope by means of a bellows or diaphragm arrangement 5. Normally each electrode consists of a contact assembly 6 fixed to a conducting rod 7 which is called a stem. By virtue of the bellows the moving stem passes through its end plate and projects beyond. One electrical connection of the circuit being switched is made to a terminal 8 attached to the end plate at the fixed contact end, which may be a continuation of the fixed contact stem through its end plate. The other connection is made to the projecting end of the stem of the moving contact, but because the stem end moves, connection has to he made by way of a flexible conductor 9 or a conductor with a sliding component.

In present designs of switchgear an actuator outside the vacuum and not at the voltage being switched is connected mechanically to the projecting moving electrode stem by virtue of a drive insulator 10, and acts to engage or disengage the moving electrode and the fixed electrode.

Our patent application GB1401824.6 describes an improved switchgear component T which a vacuum switching device is combined with an electromagnetic actuator in such a way that there are no moving parts external to the assembly and both COconductors for the circuit being switched may be connected directly to terminals 0 formed on the end plates of the device. Figure 2 illustrates one implementation of that invention, in which a flexible connector 12 inside the vacuum connects the moving contact assembly to the inside of the corresponding end plate. The winding 13 of an C\J electromagnetic solenoid is shown fixed to the end plate associated with the moving contact, and an extending tube 14 of the vacuum envelope allows a rod 15 of magnetisable material such as iron inside the vacuum to project into the winding. This rod is connected mechanically by another rod 16 to the moving contact. This rod need not he a good electrical conductor. Often the coil is formed in association with a core of magnetisable material, but this is not shown.

The present invention is a way of providing the required flexible connector for the invention just described while also satisfying some other requirements.

There are three requirements associated with the moving contact in a vacuum interrupter. The first is the need to conduct current from the moving contact to the end plate in a way that allows the contact to move. The second is the need to add a significant force to the moving contact to press it against the fixed contact when in the closed position, in order to keep the contact resistance low and also to oppose the throw-off force which arises between closed contacts when they pass a large current, and which tends to push the contacts apart. The third requirement is to provide an aligning means for the moving contact so that it moves correctly, with low friction, to press squarely onto the fixed contact, and also to oppose any misaligning forces arising from the actuator or otherwise.

The present invention consists of a design which provides a single solution to the first requirement and a contribution to meeting the second and third requirements. It may be applied to vacuum switching devices with no external moving pails as in GB1401824.6, and also to conventional switchgear or indeed any mechanical circuit breakers where it is necessary to provide one or more of movement of a conducting component, closing force and guidance.

According to the invention, which is shown in figure 3, a component called a combined spring 20 is provided, which may be within the vacuum in the case of a vacuum switching device. The combined spring is made at least partly of a low electrical resistance material, for example copper, and may be in the form of a helical spring. The two ends of this spring are connected to the end plate and to the contact assembly in ways that give good electrical contact and good conduction of heat. The number of turns of the helix and other design parameters are selected to provide low electrical resistance, the required contact force and sufficient stiffness in a lateral direction at the contact assembly end.

The helix of low electrical resistance material may be assisted by a second helical spring member made of a mechanically stiff material such as steel, which helps provide the necessary forces. This second spring 25 may be attached to the first spring, as shown in figure 4, or interleaved with it, and inside it as shown in figure 5, or outside it.

r To reduce stiffness while retaining the same thermal and electrical conductivity a CO spring may be split into two or more parallel parts as shown in figure 6. To achieve the required properties any number of different springs may be used together.

A spring need not be helical in form; it could for example have a concertina form or cantilever form or a spring washer form. C\J

O

Claims

Claims 1. A vacuum switching device consisting of an evacuated envelope which includes an insulating component, a fixed electrode and an internal moving electrode which are designed to engage and disengage mechanically to perform the switching function and which are completely enclosed within the vacuum device, whereby the moving component is connected to a electrically conducting end of the vacuum chamber by an electrically conducting spring component which allows for the movement of the moving contact while maintaining electrical connection from it to the outside of the device.
2. A vacuum switching device as in claim 1 whereby the spring component also applies a suitable force to maintain the moving contact in the closed position.
A vacuum switching device as in claims 1 or 2 whereby the spring component also provides alignment and guidance for the moving component.
4. A vacuum switching device as in claims 1, 2 or 3 whereby the spring component also provides conduction of heat from the moving component to the outside of the device.
A vacuum switching device as described in any of the above claims whereby force is provided by means of spring washers arranged so as to provide the correct force.
6. Switchgear which includes a device which provides alignment for the moving contact of a switching device, an added contact force, and an electrically conducting component which allows for the movement of the moving contact while maintaining electrical continuity.