GB2341491A

GB2341491A - Improvements in vacuum interrupters

Info

Publication number: GB2341491A
Application number: GB9919845A
Authority: GB
Inventors: Gordon James Rushton; Leslie Thomas Falkingham; Rama Shankar Parashar
Original assignee: Alstom UK Ltd
Current assignee: GE Power UK
Priority date: 1998-08-21
Filing date: 1999-08-23
Publication date: 2000-03-15
Anticipated expiration: 2019-08-23
Also published as: GB2341491B; GB9919845D0

Abstract

A vacuum interrupter comprises an evacuated envelope 11 including an insulating cylinder and electrode means comprising a stationary contact electrode 7 and a moveable contact electrode 9 housed within the envelope which are adapted to be engaged or disengaged to close or open a circuit to which the interrupter is connected. Each of the electrode means comprises a coil defining means which in use is adapted to generate magnetic fields to control the formation of arcs when the electrode means are disengaged. The coil defining means comprises a tapered portion 22 supporting a contact means 28, the tapered portion tapering from a wider portion to substantially the width of the contact means. Slits 30 are provided in the tapered portion.

Description

2341491 IMPROVEMENTS IN VACUUM INTERRUPTERS This invention relates to

improvements in vacuum interrupters for electric circuits.

Known vacuum interrupters comprise an evacuated envelope including an insulating cylinder and electrode means comprising a stationary contact electrode and a moveable contact electrode housed within the envelope, the electrodes being adapted to engage or disengage to close or open a circuit to which the interrupter is connected, each of the electrode means comprising a coil defining means which in use is adapted to generate magnetic fields to control the formation of arcs when the electrode means are disengaged. Such known interrupters will hereinafter be referred to as "interrupters of the kind set forth". Examples of such interrupters are shown in US 4 532 391, EP 0 155 376 and EP 0 329 410.

However, known interrupters do not necessarily form a magnetic field to give as efficient control of the formation of the arc as is desired.

According to the invention in a vacuum interrupter of the kind set forth the coil defining means comprises a tapered portion supporting a contact means, the tapered portion tapering from a wider portion to substantially the width of the contact means.

Such an interrupter has the advantage that the magnetic field generated by the coil defining means has better characteristics and leads to better control of the arc as it forms when the electrode means are disengaged.

The tapered portion may be angled substantially in the range of 300 to 750 from a plane normal to a plane of an end face of the contact means. More 2 preferably the tapered portion may be angled at substantially 450 from a plane normal to a plane of an end face of the contact means. Altering the angle of the tapered portion has the affect of changing the magnetic field formed so that the arc forming on disengagement of the electrode means 5 can be controlled as desired.

The tapered portion may have a hollow portion wall portions. The wall portions of the tapered portion may have formed therein at least one slit. Preferably there are a plurality of slits. In the preferred embodiment there may be three slits formed in the wall portions. Such slits provide the means to form the magnetic field to control the arc.

Conveniently the hollow portion is substantially cylindrical. Preferably the walls of the cylinder are arranged substantially parallel to an axis of the interrupter. Such a structure is advantageous because it prevents current flowing in the region occupied by the hollow portion. Such prevention of current flow is in itself advantageous because it helps to provide a suitable magnetic field to provide the desired interruption characteristics.

The slit may run from a region of the tapered portion adjacent the contact means at an angle to the contact means. The angle of the slit to the contact means may be substantially in the range of 5" to 450. In the preferred embodiment the angle of the slit to the contact means may be C.

Preferably the slit is provided entirely through the wall portion from the hollow portion to an outside face region of the wall portion. Such a structure is advantageous because it prevents currents by-passing the slit, and forces currents flowing in the wall portions to flow along paths 3 defined by the slit or slits. Thus, the slits can be formed to control current flow and thus formation of the magnetic field can be controlled.

The contact means may be fabricated from a material different from that of the tapered portion. This has the advantage that the path of the electric current flowing through the electrode means is modified to increase its flow through the coil defining means.

The tapered portion may be fabricated from copper or copper alloys. The contact means may be fabricated from CuCr or WC-Ag. The skilled person will appreciate that other materials will be suitable.

The configuration of the electrode means may be adapted, in use, to ensure that the magnetic field produced to control the arc has the same polarity over the whole of the contact means. Prior art vacuum interrupters suffered from the problem that the strength of the magnetic field decayed from a central region of the contact means towards the edge regions and even reversed in polarity at the edge regions. This is somewhat disadvantageous in that the arc formed when the contact means are disengaged is not as adequately controlled as may be desired.

The contact means may comprise any one of the following shapes: a disc, a cup shaped portion, an annular ring, an annular portion combined with a disc portion.

The tapered portion may have a width of up to substantially 20Omm. More preferably the tapered portion may have a width of up to substantially 150mm.

4 The electrode forming means may be adapted to form a magnetic field which is in an axial direction of the current flowing through the electrode means; an axial field vacuum interrupter. Alternatively, the electrode forming means may be adapted to form a magnetic field which is normal to the current flowing through the electrode means; a radial field vacuum interrupter.

If the electrode means is adapted to form an axial field the slits in the tapered portion of the stationary contact electrode are preferably inclined at substantially the same angle relative to the contact means as the slits in the moveable contact electrode. However, if the electrode means is adapted to form a radial field the slits in the tapered portion of the stationary contact electrode are preferably inclined at substantially 1800 minus the angle at which the slits in the tapered portion of the moveable contact electrodes are inclined relative to the contact means.

The electrode means may be provided with a cover to protect the slits from any damage caused by the arcs.

The cover material may be of copper or copper alloy.

There now follows by way of example only a detailed description of the invention with reference to the accompanying drawings of which:

Figure 1 shows a typical arrangement of a vacuum interrupter; Figure 2 shows a side elevation of a contact electrode according to the present invention; Figure 3 shows the contact electrode of Figure 1 with a portion cut away; Figure 4 shows the contact electrode of Figure 1 with a cover; 5 Figure 5 shows a graph of the electric field between two contact electrodes as shown in Figures 1 and 2 versus. displacement from a centre region of the contact electrode; and

Figure 6 shows a cross section through the contact electrode of Figure 2.

A typical arrangement for a vacuum interrupter is shown in Figure 1 wherein an evacuated envelope 11 comprising an insulating cylinder 1, with metallic end plates 2, 3 joined to opposite ends of the insulating cylinder 1. Within the cylinder 1 there is provided a stationary contact 7 and a moveable contact 9. Each of the contacts 7, 9 has an electrode means at an end portion comprising a coil forming means 6, 8 and an engagement means 13, 14.

The contact electrode 20 of Figure 2 comprises a tapered portion 22 with first 24 and second 26 oppositely inclined co-axial frusto conical portions having their wider base portions adjacent one another. A contact means 28 is supported by the second frusto conical portion 6 and has formed therein three slits 30 (only one of the slits is shown in the Figure).

The slit 30 is inclined at 80 relative to the contact means 22 and runs from near to the contact means toward the first frusto conical portion 24. Although not visible in the Figure there are three slits arranged in the 6 second frusto conical portion 26 starting at 120' intervals around the circumference of the tapered portion.

As can be seen in Figure 3 the contact means 28 comprises an insert into the second frusto conical portion 26. In this embodiment the contact means 28 comprises a disc region 32 which is adjacent an annular region 34 and it is the annular region which is inserted into the second frusto conical portion 26.

In Figure 6 a hollow portion 36 can be seen at a centre region of the contact electrode 20 with wall portions 38 forming one of the frusto conical portion of the contact electrode 20. The hollow portion 36 is cylindrical in shape and substantially co-axial with the axis of the contact electrode 20. As can also be seen in Figure 6 the slit 30 passes entirely through the wall portions 38 running from an outside surface to the hollow portion 36.

The contact means 28 is fabricated from CuCr whilst the tapered portion 22 is fabricated from Cu.

A graph showing electric field intensity on the vertical axis versus. displacement radially from a centre region of the contact means 28 is shown at the centre of Figure 5. It will be noted that the electric field intensity has a maxima toward the centre region of the contact means 28 and decreases toward outer regions (regions at large radial displacements from the centre region). Indeed, at radial displacements larger than the contact means 28 but within the diameter of the tapered regions 22 the electric field reverses polarity. However, the skilled person will appreciate that the field has a positive (in the graph shown) intensity over the whole of contact means 28.

7 Further, it will be noted that the electrode means of the stationary contact 7 and the moveable contact 9 both have a slit 30 which is inclined at 8" to the contact means of the moveable contact 9. Thus an axial magnetic field will be generated by current flowing through the electrode means. In other embodiments it may be possible to incline the slit 30 of one of the electrodes at an angle of 172" to the contact means 28 so forming a radial magnetic field when current flows through the electrode means. The skilled person will appreciate the differences between the axial and radial field vacuum interrupters.

In use, alternating (AC) current passes between the stationary contact 7 and the moveable contact 9 when the contact means 28 are engaged. To interrupt the flow of current the contact means 28 are disengaged. As the current begins to build in the alternating current an arc is formed between the contact means 28 which extinguishes at current zero. A ring of lower electrical conductivity material is placed in an annular region 34 to provide mechanical stability. The ring could be of steal, ceramic or other refractory material. The ring material is not as good a conductor as the Cu of the tapered portions 22 and thus current is encouraged to flow through the coil defining / tapered portions.

Flow of the current through the coil defining portions causes a magnetic field to be formed which acts upon the arc created between the contact means 28 to control the arc.

Despite the arc being controlled by the magnetic field the contact means 28 will gradually be eroded by the formation of the arc. Such erosion will not affect the electrical properties of the coil defining means and will therefore not effect the magnetic field produced; the magnetic

8 field is produced by the tapered portions and is not affected by erosion of the contact means 28.

In the modification shown in Figure 4 a cover 35 of copper or copper alloy is provided on the electrode means to protect the slits 30 from damage caused by the arcs.

Claims

9 CLAIMS

1 A vacuum interrupter comprising an evacuated envelope including an insulating cylinder and electrode means comprising a stationary contact electrode and a moveable contact electrode housed within the envelope which are adapted to be engaged or disengaged to close or open a circuit to which the interrupter is connected, and each of the electrode means comprising a coil defining means which in use is adapted to generate magnetic fields to control the formation of arcs when the electrode means are disengaged wherein the coil defining means comprises a tapered portion supporting a contact means, the tapered portion tapering from a wider portion to substantially the width of the contact means.

2. An interrupter according to claim 1 wherein the tapered portion is angled substantially in the range of 300 to 75 from a plane normal to a plane of an end face of the contact means.

3. An interrupter according to claim 1 or 2 wherein the tapered portion has a hollow portion and wall portions.

4. An interrupter according to claim 3 wherein the hollow portion is substantially cylindrical in shape.

5. An interrupter according to claim 4 wherein the axis of the hollow portion is substantially co-axial with an axis of the interrupter.

6. An interrupter according to any one of claims 3 to 5 wherein the wall portions of the tapered portion have formed therein at least one slit.

7. An interrupter according to claim 6 wherein there are a plurality of slits.

8. An interrupter according to claim 7 wherein the slit runs from a region of the tapered portion adjacent the contact means at an angle to the contact means.

9. An interrupter according to claim 8 wherein the angle of the slit to the contact means is substantially in the range of 5' to 3T.

10. An interrupter according to claim 9 wherein the angle of the slit to the contact means is 80.

11. An interrupter according to any one of claims 6 to 10 wherein the slit or slits pass entirely through the wall portion from the hollow portion to an outer face region of the wall portion.

12. An interrupter according to any preceding claim wherein the contact means is fabricated from a material different from that of the tapered portion.

13. An interrupter according to any preceding claim wherein the tapered portion is fabricated from copper, or copper alloy.

14. An interrupter according to any preceding claim wherein the contact means is fabricated from CuCr, or WC-Ag.

15. An interrupter according to any preceding claim wherein the configuration of the electrode means is adapted, in use, to ensure that the magnetic field produced to control the arc has the same polarity over the whole of the contact means.

16. An interrupter according to any preceding claim wherein the contact means comprises any one of the following shapes: a disc, a cup shaped portion, an annular ring, an annular portion combined with a disc portion.

17. An interrupter according to any preceding claim wherein the 10 tapered portion has a width of up to substantially 20Omm.

18. An interrupter according to any preceding claim wherein the tapered portion may have a width of up to substantially 10Omm.

19. An interrupter according to any preceding claim wherein the electrode forming means is adapted to form a magnetic field which is in an axial direction of the current flowing through the electrode means; an axial field vacuum interrupter.

20. An interrupter according to claim 19 wherein the slits in the tapered portion of the stationary contact electrode are inclined at substantially the same angle relative to the contact means as the slits in the moveable contact electrode.

21. An interrupter according to any one of the preceding claims wherein the electrode forming means is adapted to form a magnetic field which is normal to the current flowing through the electrode means; a radial field vacuum interrupter.

12

22. An interrupter according to claim 21 wherein the slits in the tapered portion of the stationary contact electrode are inclined at substantially 180 minus the angle at which the slits in the tapered portion of the moveable contact electrodes are inclined relative to the contact means.

23. An interrupter according to any preceding claim wherein a cover is provided to the tapered portion of the contact electrode

24. An interrupter substantially as described herein with reference to the accompanying drawings.