GB2209094A

GB2209094A - Contact means for a vacuum switch

Info

Publication number: GB2209094A
Application number: GB8819645A
Authority: GB
Inventors: Gerhard Harz; Manfred Niegl
Original assignee: Sachsenwerk Licht und Kraft AG; Sachsenwerk AG
Current assignee: Schneider Electric Sachsenwerk GmbH; VEM Sachsenwerk GmbH
Priority date: 1987-08-26
Filing date: 1988-08-18
Publication date: 1989-04-26
Also published as: GB8819645D0; JPS6471029A; DE3728400C1

Description

1 2209094 CONTACT MEANS FOR A VACUUM SWITCH The present invention relates

to contact means for a vacuum switch.

Contact means for that purpose is disclosed in DE-OS 34 33 155. The contacts in that case each consist of a contact carrier forming the side wall of a cylindrical chamber which is subdivided into several current paths by slots inclined relative to the axis of the respective contact and covered by a contact plate.

A profile member of ferromagnetic material with a substantially cylindrical outer circumference is placed in the chamber and can have a small gap relative to the internal diameter of the chamber. A homogeneous magnetic field is to be generated in the gap between the opening contacts under the effect of an electrical current. The manufacture of the contact, in particular the application of the inclined slots and the mounting of the profile member, is difficult. Moreover, heating of the current -conduct in g windings of the contact means gives rise to problems, because heat dissipation in vacuum switches is provided not convectively, but only by radiation and heat conduction. In this connection, the small gap given by the difference in the diameters of the profile member and the chamber represents a very great thermal resistance.

According to this known contact means, the distribution of the magnetic flux in the contact gap in a part of the construction shall be made uniform through an enlargement, facing the contact disc, of the diameter of the profile member. However, the magnetic field is strongly reduced by eddy currents produced in, in particular, the contact base and the ferromagnetic profile member. The step resulting from the enlargement reduces the cross-section of the current paths

1 and because of the described heating problems cannot be so long as to give rise to a uniform flux density which, at the transition to the contact disc, reaches its rim zone.

Through slotting of the contacts at an inclination to the axis, there results an equally inclined direction of the currents flowing through the individual segments. However, only the current component directed perpendicularly to the contact axis is effective for the production of the axial magnetic field, whilst the other component extends parallel to the direction of the magnetic field. In the case of an angle of about 45' between the contact axis and the current direction, only 70% of the current contributes to the induction of the magnetic field.

There is thus scope for improvement of the electromagnetic efficiency and evening-out of the magnetic field in the contact gap as well as increase in the heat removal from the current-conducting - parts.

contact According to the present invention there is provided contact means for a vacuum switch, comprising two coaxial oppositely disposed contacts each having a cylindrical outer circumference and each com- prising an electrically conductive stud provided with a hub, a magnet body, a plurality of conductor members which are electrically connected to the hub by way of ribs and which gaplessly surround the magnet body, insulating or low-conductivity insert means partially bounding the conductor members, and a contact plate so connected to at least one of the magnet body and the insert means and electrically connected to the conductor members that current flow to the contact plate takes place substantially by way of passage means in the magnet body or the insert means, the magnet body providing relatively high resistance to current flow therethrough from the conductor portions.

In a preferred embodiment the conductor members are constructed as single layer or multi-layer coil-shaped windings or part windings, which are each arranged in a plane which is preferably perpendicular or slight inclined to the contact axis. The conductor members gaplessly surround the magnet body and are bounded by the envelope surfaces of the magnet body and by inserts of insulating or poorly conducting material, which can be connected therewith. The contact plate is so connected with the adjoining magnet body and/or with an insert separating the conductor members from the contact plate that the current flow takes place mainly in a sector-shaped passage of the magnet body or of the insert. The conductor members and the hub together with the magnet body can form a solid block contact. The electrical resistance of the current path, which leads through the magnet body and lies in shunt with the conductor members, is comparatively large, and the hub is conductively connected with each conductor member by way of a narrow rib corresponding approximately to the height of a conductor member. The magnet body is thus used in close, gapless contact of surrounding current conductor members which are arranged in the form of windings or parallelly connected part windings and thus produce an axial magnetic field. The windings extend in such a manner that the current flow takes place substantially in planes extending perpendicularly to the contact axis and thus contributes by its total value to the induction of the magnetic field. The conducting connection between the hub and the individual conductor members in that case takes place by way of relatively narrow ribs, which restrict the generation of eddy currents - 4 and reduce the phase displacement connected therewith between the main current and the magnetic field strength.

The construction described in the German (Fed. Rep.) patent specification 31 50 168 can be used for the structuring of the contacts, i.e. a cast part of high conductivity and subdivided into current paths by cast-in inserts of a material of low conductivity. The magnet body can in that case also be cast in or, for example, be soldered, glued or otherwise gaplessly connected to the subdivided conductor members.

The magnet body is preferably so constructed that, optionally with the aid of an insulating layer at at least one transition surface, it largely prevents an electrical shunting of the current and fully uses the latter for the production of the magnetic field.

Another possibility for suppression of shunting consists in the use of anti f erromacneti c substances (ferrites) for the production of the magnet bodies. According to "Grundlagen der ElektrotechniV, Philippow, VEB-Verlag Technik, (1984), pages 398 and 399, their particularly useful properties are the simultaneous provision of high permeability, low hysteresis losses and high specific resistance. The low hysteresis losses signify a low remanence, which is of Significance for a vacuum switch operating with an axial magnetic field.

Through the construction as block contact without gaps between the magnet body and the conductor members, an effective heat removal from the latter in the direction of the current stud as well as a rigid mechanical construction is provided.

The magnet body is preferably in intimate connection with the conductor member material so that no additional heat transfer resistance arises. Preferably, the magnet body is so shaped that an almost uniform z - 5 distribution of the magnetic flux density arises over the entire surface of the contact plate without the cross-sections of the conductor members, which may be of any desired shape, having to be unacceptably small. Moreover, the transfer surface between magnet body and conductor members can be further enlarged, for examole by suitable profiling.

Con-tact means embodying the invention may thus permit the magnet bodies together with the conductor members to be constructed optimally in respect of high current carrying capacity, efficient utilisation of the current for production of the magnetic field, and uniform distribution of an axial magnetic field over the contact surface, while forming a solid block contact.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

is Fi g. 1 Fi g. 2 Fi 9. 3 Fi 9. 4 Fi 9. 5 Fig. 6 Fi 9. 7 Fi g. 8 Fi 9. 9 is an elevation cf a contact in first contact means embodying the invention; is a vertical section on the line A-A of Fig. 3; is a crosssection on the line O-D of Fig. 1; is a cross-section on the line E-E of Fig. 1; is a cross-section on the line F-F of Fig. 1 and on the line U-U of Fig. 11; is a vertical section similar to that on line A-A of Fig. 3, but with changed shape of a core of the contact; is a vertical section similar to that on the line A-A of Fig. 3, but with a circularly shaped contact plate; is a plan view of the contact of Fig. 7; is a vertical section, on the line N-N of Fig. 10, of Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fi g. 14 Fi g. 15 Fi g. 16 Fi g. 17 Fi g. 18 a contact of further contact means embodying the invention; is a cross- section on the line M-M of Fig. 9; is an elevation of a contact of yet another contact means embodying the invention; is a vertical section on the line PP of Fig. is a cross-section on the line Q-Q of Fig. 11; is a cross-section on the line R-R of Fig. 11; is a cross-section on the line 5-S of Fig. 11; is a cross-section on the line T-T of Fig. 11; is a vertical section similar to that on the line A-A of Fig. 3, but with a magnet body of several concentric cylinders; and is a vertical section similar to that on the line A-A of Fig. 3, but with an insulating layer around the magnet body of the contact.

Referring now to the drawings, there is shown in Fig. 1 contact means comprising two contact bodies 1 with a contact gap 16 therebetween and with a diffuse arc L of current i and field lines of the magnetic flux density B in this gap. The construction of one of the contacts of this contact means is explained by reference to Figs. 1 to 5. The contact body 1 consists of a magnet body 2 in the form of a circular ring, conductor members 5 of the excitation coil surround ing the magnet body for the magnetic field, inserts 3a and 3b and a contact plate 7. The contact body 1 is in conductive connection by way of ribs 8 and a hub 11 with a current stud 6.

The envelope surface 4 of the magnet body 2 is inclined towards 1 - 7 the contact axis. In this manner, the contact area with the surrounding members 5 increases for a given height h, which provides a corresponding reduction in the thermal transfer resistance. The magnet field lines can enter into the contact gap 16 through the contact plate 7 and are distributed almost uniformly over the entire width. The crosssection of each member 5 is a trapezium, which narrows towards the contact plate 7 and is separated therefrom by the insert 3a in the form of a circular ring. The insert 3a is recessed (Fig. 3) at passages 9 in'order to permit current flow to the contact plate 7. The separat- ion of the individual conductor members 5 from each other is performed by the inserts 3b, which are parallel to the axis. The inserts 3a and 3b consist of insulating material or a material of high electrical resistance. The height h of the members 5 should preferably be greater than the mean width Smit of a member 5 in order for a given diameter b to be able to produce the greatest possible magnetic flux 0. Because of the trapezium shape of the member 5 and the corresponding shape of the magnet body 2, the entire contact gap 16 is penetrated almost uniformly by the magnetic field 0. The heat flow lw entering into the magnet body 2 issues, towards the axis, into the hub 11 and is conducted away by means of the current stud 6. In this manner, the heat flow Iw contributes by way of the magnet body 2 to reduction in the temperature of the members 5 parallelly to the ribs 8, which conduct current and themselves produce heat losses.

In operation, the current i flows from the stud 6 to the lower part of the contact body 1, where it is divided up into four currents il, i2, i3 and i4. These flow by way of the ribs 8 to the conductor members 5 and from there by way of the passages 9 to the contact plate 7. Due to the current f 1 ow i n the members 5, a magneti c f i el d 0 i s induced in the magnet body 2 and issues from the contact plate 7 almost parallelly to the contact axis. In co-operation with a second switch contact (Fig. 1) of like kind, a homogeneous axial magnetic field is thus produced.

Fig. 6 shows another embodiment in which the magnet body 12, for enlargement of the contact area, has a groove 10 and an inward prolongation 12a, which is disposed in contact with the hub 11. At the level of the ribs 8, the groove 10 is recessed towards the hub 11 for enlargement of the passage cross-sections for the respective currents il to i4.

A switch contact in which a circularly shaped contact plate 17 is connected with a plate-shaped magnet body 22 is illustrated in Fig. 7. The magnet body 22 is provided on the side of the hub 11 with a recess 14 by which an increase in the heat-conducting transfer surface shall be provided. For the avoidance of eddy currents, the contact plate 17 is provided with slots 15, as is apparent from Fig. 8.

A further possibility for heat removal from the members 5 of a switch contact is shown in Figs. 9 and 10. The magnet body comprises sector-shaped cores 18 which are fastened to a continuous insert 23a and separated by an intermediate space 19 in the prolongation of the ribs 8. The conducting connection from the hub 11 to the members 5 in this case takes place by way of a relatively large cross-section which itself has only a low heat loss. Through this connection, a part of the heat flow can flow out of the members 5, the other part taking its path in the already described manner through the cores 18. The contact plate 7 is mounted on the other side of the insert 23a, 1 the latter in that case having a recess at the level of the passages 9 for the conductive connection with the members 5.

It is also possible to equip a switch contact with multi-layer coil windings and thus produce an effective axial magnetic field even for small short-circuit currents. An embodiment for this purpose is shown in Figs. 11 to 16, wherein two layers are provided one above the other and each conductor member is flowed through by a quarter of the entire current. The basic construction of such a switch contact again provides a contact body 31, which is connected with a current stud 6 and terminated by a contact plate 7. Starting out from this contact plate 7, the following components follow one another in axial direction:

a continuous insert 32a with passages 33a, according to Fig. 13, for the electrical connectiontothe contact plate 7, - the upper layer of the conductor members 34 separated from each other by inserts 32b, which are parallel to the axis as well as the cylindrical magnet body 36, according to Fig. 14, - a second continuous insert 32c with passages 33b, according to Fig. 15, for electrical connection between the upper and the lower layer of the conductor members 34 and 35, according to Fig. 15, - the lower layer of the members 35 separated from each other by inserts 32d which are parallel to the axis as well as the sector-shaped magnet members 37 and passages 38, according to Fig. 16, which are arranged therebetween and connected with the ribs 8, and - the hub 11 with the ribs 8, according to Fig. 5.

The course of the current il is shown in Figs. 12 to 16. For the sake of simplicity, the construction of the magnet members 36 and 37 is cylindrical and planar; other shapes, as shown in the other Figures, are also usable. The inserts 32a and 32c, in the form of circular rings, in that case have the task of bounding the layers 34 and 35 of the conductor members and of connecting the magnetic members 36 and 37 together. They can consist of the same material as the members 36 and 37.

In order to achieve a uniform distribution of the magnetic flux density B, it is advantageous, particularly in the case of large switch contacts, to provide several concentric magnet members 39a, 39b and 39c according to Fig. 17, in which the intensity of magnetic induction reduces inwardly from the outside.

In order to completely exclude shunt currents by way of the magnet body 2 and thus to be able to use the entire current i for the production of the magnetic field, the magnet body can be separated by an insul- ating layer 40 from the members 5 and/or the hub 11 (see Fig. 18).

It is assumed in all previously illustrated embodiments that the current i is distributed over four conductor members 5 lying in parallel. Other divisions of the current are also possible.

In all illustrated embodiments the conductor members and the hubs can be produced by casting, for example, from a highly conductive copper. In that case, the inserts 3a, 3b and 32a to d can be connected, before the casting process, with the magnet body and thus act as part of the casting mould. The magnet body and inserts in tha t case can be prefabricated as a one-piece moulded article.

It is also feasible for the conductor members to be prefabricated without the magnet body and for the magnet body to be connected in a further operating step with the resulting moulded part. The connecting t, - 11 operation can take place by, for example, gluing, soldering or a similar method.

Claims

1. Contact means for a vacuum switch, comprising two coaxial oppositely disposed contacts each having a cylindrical outer circumference and each comprising an electrically conductive stud provided with a hub, a magnet body, a plurality of conductor members which are electrically connected to the hub by way of ribs and which gaplessly surround the magnet body, insulating or low-conductivity insert means partially bounding the conductor members, and a contact plate so connected to at least one of the magnet body and the insert means and electrically connected to the conductor members that current flow to the contact plate takes place substantially by way of passage means in the magnet body or the insert means, the magnet body providing relatively high resistance to current flow therethrough from the conductor portions.

2. Contact means as claimed in claim 1, wherein the conductor members, the hub and the magnet body of each contact form a solid block contact unit.

3. Contact means as claimed in either claim 1 or claim 2, wherein the height of the ribs of each contact in the axial direction thereof is substantially equal to the height of the associated conductor members.

4. Contact means as claimed in any one of the preceding claims, wherein the conductor members of each contact are parts of a conductor body of cast material.

5. Contact means as claimed in claim 4, wherein the magnet body and - 13 the insert means of each contact are incorporated in the casting of the associated conductor body.

6. Contact means as claimed in any one of claims 1 to 3, wherein the conductor members of each contact are parts of a moulded contact body in which the insert means of that contact are incorporated, the contact body being secured to the associated magnet body.

7. Contact means as claimed in any one of the preceding claims, wherein the magnet body of each contact comprises anti f erromagneti c materi a].

8. Contact means as claimed in any one of claims 1 to 6, wherein the magnet body of each contact comprises a paramagnetic or ferromagnetic material and is provided on at least- one face thereof with a coating of insulating material.

9. Contact means as claimed in any one of claims 1 to 6, wherein the magnet body of each contact comprises a plurality of concentric magnetic members of respectively different permeability.

10. Contact means as claimed in any one of the preceding claims, wherein the magnet body of each contact has a hollow cylindrical shape and is connected to the associated hub by mans facilitating heat con- duction therebetween.

11. Contact means as claimed in any one of claims 1 to 9, wherein - 14 the magnet body of each contact has a solid cylindrical shape and is connected to the associated hub by means facilitating heat conduction therebetween.

12. Contact means as claimed in any one of claims 1 to 8, wherein the magnet body of each contact comprises a plurality of arcuate magnetic members separated from each other by conductor arms connecting the conductor members of that contact to the associated hub.

13. Contact means as claimed in any one of claims 1 to 8, wherein the outer circumference of the magnet body of each contact is so inclined relative to the axis of the contacts that the cross-section of the conductor members of that contact reduces in direction towards the associated contact plate.

14. Contact means as claimed in claim 11, wherein the maximum diameter of the outer circumference of the magnet body of each contact is substantially equal to the diameter of the associated contact plate.

15. Contact means as claimed in any one of claims 1 to 8, wherein the magnet body of each contact is provided at its outer circumference with at least one recess or projection.

16. Contact means as claimed in any one of the preceding claims, wherein the contact plate of each contact comprises a material resistant to burning-off and of low ductility.

a A 1 - 15

17. Contact means as claimed in any one of the preceding claims, wherein the contact plate of each contact has an annular shape with an inner diameter at most equal to the inner diameter of the associated magnet body.

18. Contact means as claimed in any one of claims 1 to 16, wherein the contact plate of each contact is circular and of uniform thickness.

19. Contact means as claimed in any one of claims 1 to 16, wherein the contact plate of each contact is provided at an end face thereof with a contact surface portion with an area smaller than that of the f ace.

20. Contact means as claimed in any one of the preceding claims, wherein the height of each of the conductor members of each contact in the axial direction thereof is substantially equal to the height of the associated magnet body and greater than the mean width of that conductor member.

21. Contact means as claimed in claim 1, wherein the magnet body of each contact is constructed as a plurality of layers and the associated conductor members are constructed as a corresponding plurality of layers, respective further insert means being arranged between each two adjacent layers of the conductor members and passage means being provided in each of the insert means and so arranged as to be rotationally displaced, from insert means to insert means in axial direction of the contact, by a given amount plus the thickness of such an insert means.

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22. Contact means as claimed in claim 5, wherein the magnet body of each contact is secured to the insert means and incorporated as a unit in the casting of the associated contact body.

23. Contact means as claimed in claim 22, wherein the magnet body of each contact is additionally secured to the contact plate and incorporated, together with the insert means, as a unit in the associated contact body.

24. Contact means as claimed in any one of claims 1 to 8, wherein the magnet body and the insert means are formed from a workpiece.

25. Contact means substantially as hereinbefore described with reference to Figs. 1 to 5 of the accompanying drawings.

26. Contact means substantially as hereinbefore described with reference to Fig. 6 of the accompanying drawings.

27. Contact means substantially as hereinbefore described with reference to Figs. 7 and 8 of the accompanying drawings.

28. Contact means substantially as hereinbefore described with reference to Figs. 9 and 10 of the accompanying drawings.

29. Contact means substantially as hereinbefore described with reference to Figs. 11 to 16 of the accompanying drawings.

1 k.

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30. Contact means substantially as hereinbefore described with reference to Fig. 17 of the accompanying drawings.

31. Contact means substantially as hereinbefore described with reference to Fig. 18 of the accompanying drawings.

Published- 1988 at Tte Pater. office. S.a.,e House 66 7' Ilicl- Hcltz:,.F-a:,ther c2r,.e= be obtaine:l f c=. The Patent Office.

- Lonacn WC1R 4TP r Sales Branch. St Mary Cray. Orpington- Kent BR5 3RD Printed by Multiplex techniTues ltd. S. MarY CraY. Ker,, COn 1187.