GB2507262A

GB2507262A - Spiral contact coil for vacuum switch

Info

Publication number: GB2507262A
Application number: GB1218975.9A
Authority: GB
Inventors: Leslie T Falkingham
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-10-23
Filing date: 2012-10-23
Publication date: 2014-04-30
Also published as: GB201218975D0; GB2511373A; GB2511373B; GB201318392D0

Abstract

A vacuum switching device comprises an evacuated envelope having an insulator; a fixed electrode and a moving electrode which engage and disengage mechanically to perform switching and which include a contact comprising a coil assembly behind a contact disc. The coil assembly has between one and five arms which follow a curved path from a centre electrode to the outer diameter of the contact disc. The coil can have two, three or four arms whose spiral path covers between 200, 130, 100 and 80 degrees of rotation respectively. The coil assembly can have radiused corners and edges to improve the voltage performance. The coil provides self-generated axial magnetic fields in the axis of the contact gap in order to make an arc diffuse over the contact surface at high currents.

Description

Improvements Relating to Vacuum Swilehing Devices

DESCRIPTION

Improvements Relating to Vacuum Switching Devices Prior Art; US 3 946 179, US 4588879, GB 2231 723, US 4698467 This invention relates to improvements in vacuum switching devices, which may include for example vacuum interrupters or vacuum switches.

A simplified schematic diagram of a typical vacuum switching device is shown in figure 1. Vacuum switching devices generally consist of an evacuated envelope, which includes an insulating component (a), a fixed electrode assembly (b), and a moving electrode assembly (c), which consist of a conducting rod (d) and a contact assembly (e).The electrodes are designed to engage and disengage mechanically to perform the switching function. This movement is permitted without breaking the seal of the evacuated envelope by means of a bellows or diaphragm arrangement (f). At low currents the current arc passing from one contact disc (g) to the other is diffuse, that is it is spread over the contact surfaces. Above a current of a few thousands of amps, due to aspects of the physics of the vacuum arc, the arc constricts into a narrow column.

When switching large currents it is necessary to prevent arc constriction which would cause overheating of parts of the contact surfaces and inhibit successful interruption of the current. Vacuum switching devices that are designed to switch large currents have been produced for many years. A number of different designs of electrode assemblies have been proposed to switch the current on or off under low current and high current conditions. Examples of such designs may be seen in EP 0349303, DE 3915519, DE 3610241, GB 238111 A. These designs use self-generated magnetic fields to control the arc. Figure 2 shows construction features common to some of these electrode assemblies. The conducting rod (d) carries current to an arm conductor (h) that carries current via pillars (i) to the contact disc (g). Current is then carried across the vacuum to the other electrode disc by one or more arcs Q). The configuration of cut-rent flow produces a desired configuration of magnetic field in the space between the contact discs and this magnetic field prevents constriction of the arc-The arm conductor assemblies are also known as coil assemblies.

This invention relates to one particular type of prior art contact geometry as typified by US 39946179. Figure 3 shows an exploded view of this geometry. The current path in the coil (h) is radial from the centre to the periphery of the contact at which point it I, turns to follow the curve of the outside diameter of the contact disc. The design of coil assembly in US 39946179 is shown in plan view in figure 4.

This current flow produces a magnetic field which is in the direction of the axis of the contact and this field acts to prevent the constriction of the arcs (j) produced between the contacts during interruption of current, and thereby allows the contacts to interrupt higher levels of current successfully.

This prior art geometry gives an axial magnetic field which is essentially concentrated at the outside diameter of the contact disc which has the disadvantagc that it givcs a lower field at the inner part of the contact disc. It also gives rise to eddy currents in the contact disc, which, to one skilled in the art, is known to be detrimental to the generation of the axial magnetic field, reducing its effectiveness locally.

According to the invention, an embodiment of which is shown in figure 5, the coil assemblies each include curved arm conductors to provide the path along which the current flows. In this case the current path from the rod to the contact disc follows a curved path which gives additional axial magnetic field strength at the inner part of the contact disc and also reduces the eddy current effects, thereby improving the arc control capability of the contact assembly. Because this invention allows the current to follow a longer path than previously it also increases the overall strength of the axial magnetic field due to an increase in the effective number of coil turns for each contact arm.

This invention both improves the strength of the axial magnetic field generated and smooths the magnetic field over a larger surface area of the contact disc with a result that a higher current can be successfully interrupted for a given size of contact diameter, thereby making the vacuum switching device smaller and of lower cost.

An additional benefit of the invention is that the use of a curved arms, as opposed to arms which include a sharp change in direction, much reduces electrostatic stress fields and thereby provides improved voltage performance for the vacuum switching device which is particularly advantageous for high voltage applications.

The invention may bc applied to the design of vacuum switching devices over a wide range of contact diameters, the actual diameter chosen depending to a great extent on the intended maximum currcnt to be interrupted, and the maximum load current intended to be carried.

A person skilled in the art will appreciate that this invention may be applied to variations of this basic geometry from one arm to many arms.

Claims

CLAIMS1. A vacuum switching device consisting of an evacuated envelope which includes an insulating component, a fixed electrode and a moving electrode which are designed to engage and disengage mechanically to perform the switching function and which includes at least one contact with a coil assembly behind the contact disc whereby the coil assembly has between one ann and five arms and the arms follows a curved path from the centre electrode to approximately the outside diameter of the contact disc.
2. A vacuum switching device as described in Claim 1 whereby the coil assembly has two arms and the spiral path covers more than 2000 of rotation.
3. A vacuum switching device as described in Claim 1 whereby the coil assembly has three arms and the spiral path covers more than 1300 of rotation.
4. A vacuum switching device as described in Claim 1 whereby the coil assembly has four arms and the spiral path covers more than 1000 of rotation.
5. A vacuum switching device as described in Claim I whereby the coil assembly has five arms and the spiral path covers more than 80° of rotation.
6. A vacuum switching device as described in claim 1 whereby the coil assembly has radiused corners and edges to improve voltage performance.