ELECTRICAL INTERRUPTION DEVICE

Abstract

An electrical interrupter device for switching a short-circuit electrical current in an electric circuit is disclosed. The device comprises a vacuum evacuated housing (58); first and second electrodes (54, 56) at least partially located within the housing. The first and second electrodes (54, 56) are separated by a rail gap. A third electrode (52) moveable relative to the first and second electrodes (54, 56) between a closed circuit position and an open circuit position is provided, whereby an electrical arc is generated between the third electrode (52) and at least one of the first and second electrodes (54, 56) during said movement. Once generated, the arc is directed by the first and second electrodes (54, 56) away from the third electrode (52).

Claims

1. An electrical interrupter device for switching a short-circuit electrical current in an electric circuit, said device comprising: a vacuum evacuated housing; first and second electrodes at least partially located within the housing, said first and second electrodes separated by a rail gap; a third electrode moveable relative to the first and second electrodes between a closed circuit position and an open circuit position, whereby an electrical arc is generated between the third electrode and at least one of the first and second electrode during said movement; wherein the arc is directed by the first and second electrodes away from the third electrode.

2. The device according to claim 1, wherein the first and second electrodes are non-circular.

3. A device according to claim 1, further comprising a fourth electrode opposing said third electrode, wherein the third electrode is moveable relative to the fourth electrode and wherein the third and fourth electrodes are in contact in the closed circuit position and are separated by an arc gap in the open circuit position.

4. A device according to claim 3, wherein movement of the third electrode relative to the fourth electrode generates the electrical arc in the arc gap.

5. A device according to claim 4, wherein the arc is transferred from the arc gap to the rail gap when the third electrode moves a distance further away from the fourth electrode than the distance of the rail gap.

6. The device according to claim 1, wherein the first and second electrodes act as electrical rails to direct the arc.

7. A device according to claim 6, wherein the rails are substantially linear.

8. A device according to claim 6, wherein the rails are substantially parallel.

9. A device according to claim 6, wherein the rails are divergent.

10. A device according to claim 6, wherein at least a portion of the rails are trumpeted.

11. A device according to claim 1, wherein the third electrode is integrated with either the first and second electrode, and wherein the third electrode moves to separate the first and second electrodes in a scissor action.

12. A device according to claim 1, wherein the first electrode is substantially tubular and the second electrode is a rod that sits within the first electrode.

13. A device according to claim 12, wherein the first electrode is substantially, spiralled or curved.

14. A device according to claim 1 wherein the first and second electrodes are helically aligned.

15. A device according to claim 1 wherein the arc is directed towards an arc quenching means.

16. A device according to claim 15, wherein the arc quenching means comprises an arc baffle plate target, and wherein the arc is directed to the target for dissipation.

17. A device according to claim 15 wherein the arc quenching means comprises arc splitter plates.

18. A device according to claim 17, wherein the arc splitter plates comprise a plurality of substantially parallel quenching plates, said quenching plates intended to divide the arc into a corresponding plurality of smaller arcs, each smaller arc driven between two quenching plates.

19. A device according to claim 1, wherein the electrodes comprise one or more slots, each slot oriented to produce a magnetic field across the electrodes.

20. A device according to claim 19, wherein the magnetic field acts to drive the arc along the electrodes.

21. A device according to claim 1, wherein the device is a vacuum interrupter.

22. A device according to claim 21, wherein the first and second electrodes are wholly located within the housing such that movement of the electrodes to perform a switching function occurs solely within the housing.

23. A device according to claim 1, wherein the electrical current load is a direct current load.

24. The device of claim 1, wherein at least one of the first and second electrodes are non-circular, such that the electrical arc is directed along the non-circular electrode.

Description

DETAILED DESCRIPTION

[0051] For a more complete understanding of the features and advantages of the present disclosure, reference is now made to the detailed description along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:

[0052] FIG. 1 is a prior art vacuum interrupter;

[0053] FIG. 2 is an illustration of axial electrical electrodes or contacts suitable for use with the vacuum interrupter of FIG. 1;

[0054] FIG. 3 is an illustration of radial electrical contacts suitable for use with the vacuum interrupter of FIG. 1;

[0055] FIG. 4 is an illustration of a linear vacuum interrupter according to the present invention;

[0056] FIG. 5 is an illustration of an alternative linear vacuum interrupter according to the present invention with electrical contacts equivalent to the radial electrical contacts of FIG. 3;

[0057] FIGS. 6a-6c are illustrations of a pair of electrical contacts when closed (a), initially opened (b) and a fixed time later (c);

[0058] FIG. 7 shows an alternative configuration of the electrical contacts of FIG. 6;

[0059] FIGS. 8a and 8b show a configuration of electrical contacts according to an embodiment; and

[0060] FIGS. 9a and 9b show an alternative configuration of electrical contacts according to another embodiment.

[0061] FIG. 4 illustrates a simple linear interrupter in partial section view, said interrupter comprising contacts 41 enclosed within a housing 43. The housing is generally vacuum evacuated and is sometimes referred to as an envelope. The vacuum interrupter comprises electrodes or contacts 41 which have slots 42 oriented to produce magnetic field across the width of the contacts, so that when an electrical current is passed through the contacts and the contacts separated an arc is formed. The electrical contacts 41 thus are designed to engage and disengage mechanically to perform a switching function. Normally this movement is permitted without breaking the seal of the evacuated envelope 43 by means of a bellows or diaphragm arrangement 44. In the example shown the arc is moved by the motor effect along the length of the contacts. The length is chosen to be sufficient to control the arc until it extinguishes. This may be called a transverse field linear contact and is to some extent equivalent to a radial field circular contact. The contacts 41 are enclosed within an insulating vacuum enclosure 43. This may for example be in the form of an insulating container of lunch box shape 43, sealed shut on one side by a generally rectangular lid (not shown). Shields which prevent deposition of metal vapour are also not shown. The moveable contact passes through the vacuum enclosure via a bellows 44.

[0062] A simple linear interrupter whose contacts produce field perpendicular to the contact faces requires the two current paths to be offset to either side of the active contact face and is equivalent to an axial field circular contact.

[0063] FIG. 5 illustrates a linear transfer switching interrupter whose contacts are equivalent to radial field circular contacts. The continuous current contacts are on the left and consist of a fixed contact 51 and a moving contact 52 which passes through bellows 53. These contacts are shown in the open position in FIG. 5.

[0064] As in FIG. 4, the interrupter is housed within a vacuum evacuated enclosure 58 and operates broadly similar to the embodiment described above in FIG. 4. However, in this example, to make a current the contacts 51 and 52 are closed, arcing not being a problem during current make. These contacts remain closed during passage of normal current.

[0065] Adjacent to these contacts 51, 52 is one end of a pair of linear contacts 54, 56 having arc surfaces 54a, 56a. These linear contacts 54, 56 are of fixed contact gap (i.e. they are separated by a constant distance), and do not require a bellows because they are contained within the vacuum housing 58 and do not move relative to the housing 58. The lower linear contact 54 is connected by a rigid conductor 55 to the fixed continuous contact 51 and the upper linear contact 56 is connected by a flexible connector 57 to the moving continuous contact 52. The switching contacts 51, 52 are slotted in opposite directions as shown, and when current flows magnetic field in the contact gap is in a direction across the contact faces, i.e. perpendicular to the plane of the diagram.

[0066] When current break is required force is applied to the moving continuous contact 52 and as it separates from its fixed contact 51 an arc is formed between their faces. As soon as the gap, referred to as an arc gap, between these faces is wider than the gap, referred to as a rail gap, between the linear switching contacts 54, 56, the arc transfers to that gap, and the current path transfers via the rigid conductor 55 to the stem of the lower switching contact, and via the flexible contact to the stem of the upper switching contact. Because of the magnetic field produced by the current in the slots and the contact rail, the arc moves along the length of the linear contacts gap, preventing damage to the contact surfaces and facilitating current interruption.

[0067] This assembly also fits in a vacuum container which may be in the form of a lunch-box shaped ceramic with a lid which can be sealed in place.

[0068] In a variant form of the transverse field linear interrupter the slots reverse direction half way along each contact, so that the arc can oscillate back and forth along the length of the contacts.

[0069] In a variant form of the transverse field linear interrupter there are no slots, and instead the force on the arc is provided by the flow of current along the rails feeding the arc.

[0070] The geometry of a linear contact vacuum interrupter and the small depth which its vacuum container can have, make it feasible to produce the magnetic fields required with magnets placed against the outside the vacuum container. Current carrying coils may also be used, which would need to be energised only during the moments of current breaking. This arrangement can allow the bellows to be removed such that actuation of the moving contact 52 is actuated either from within the vacuum chamber or externally through the walls of the chamber.

[0071] FIGS. 6a-6c show alternative configurations for the electrodes or contacts within a vacuum interrupter. The embodiment of FIG. 6 essentially combines the switching contacts 51, 52 and the linear contacts 54, 56 of FIG. 5. FIG. 6a shows a fixed contact 61 and a moveable contact 62. The contacts 61, 62 are shown as elongate rods or bars rather than conventional circular contact plates.

[0072] Movement of the moveable contact 62 may be by an actuator, such as a permanent magnet actuator or other known mechanism. In the example shown the moveable contact pivots about a fixed point and may be actuated to pivot downward away from fixed contact 61. However, the principle of having the moveable contact move away from the fixed contact is key. In the example shown in FIG. 6a the contacts 61, 62 are in contact at point 64 such that the contacts are closed and a current flows through both contacts and no arcing is present.

[0073] In the event of an overcurrent surge or other switching event, the moveable contact 62 is actuated and moves away from the fixed contact 61. This causes the contact point 64 to be broken and an arc 65 forms between the two contacts. In a conventional vacuum interrupter having circular contacts the arc is directed by techniques as described in FIGS. 1 to 3 above. However in this embodiment the arc is instead directed away from the contact point 64 and along the contacts 61, 62. This is shown in FIG. 6c where the arc 65 has moved along both contacts 61, 62. As the arc 65 moves along the contacts the arc length increases due to the increased separation between the contacts. When the arc reaches the end of the contacts, the arc balloons outwards as shown in FIG. 6c, weakening the arc strength. This acts to dissipate the current arc, which may then be quelled or extinguished using dedicated surfaces or baffles placed and designed for such purposes. By separating the arc formation region from the arc quenching region, both regions can be tailored to maximise their functions.

[0074] FIG. 7 shows an alternative configuration of the concept explored in FIG. 6. In this embodiment the contacts 71, 72 are connected in a similar manner to described above. However, each contact 71, 72 has a trumpeted shaped end 73, 74. This has the effect that the arc 75 balloons significantly once it reaches the end of the contacts. By spreading and ballooning the arc in this manner the strength of the arc is considerably weakened. Furthermore, in the example shown, arc quenching plates 76 are shown which further extend the arc and divide it, allowing the arc to be quenched by the plates 76.

[0075] FIG. 8 shows another configuration of the contacts. In this example the fixed contact 81 surrounds or envelops the moveable contact 82. The moveable contact further comprises a rod 84 that runs within the fixed contact 81. FIG. 8b shows the contacts in a closed position where moveable contact end plate 85 is in contact within the fixed contact 81. As the moveable contact is separated from the fixed contact during a switching event, the arc travels in a circular path between the rod 84 and the fixed contact 81. In this manner, the arc may be directed away from the contact site in a controlled manner.

[0076] A final example is shown in FIG. 9. This example is similar to FIG. 8, but the fixed contact 91 is a helical shape and spirals around the rod 94 of the moveable contact 92. During arc generation, the arc is formed between the rod 94 and the helical surface of the fixed contact 91 and then travels in a helical manner around the fixed contact.

[0077] This concept of transferring or directing an electrical arc away from the point of generation allows both elements to be tailored according to their functionality, rather than being constrained by the other function. Additionally, this concept allows for vacuum switching of DC current due to the arc being directed away from the point of contact rather than continuing to flow as in conventional interrupters. By altering the geometry of the contacts to be non-circular the electrical arc generated is directed away and extended increasing the arc voltage sufficiently to collapse the arc and provide interruption.