Title of Invention

VACUUM CARTRIDGE FOR AN ELECTRICAL PROTECTION APPARATUS SUCH AS A SWITCH OR CIRCUIT BREAKER

Abstract The present invention relates to a vacuum cartridge for an electrical protection apparatus such as a switch or a circuit breaker, said cartridge comprising an enclosure of substantially cylindrical shape closed by two end plates, two contacts extending axially inside the enclosure, at least one whereof, called the movable contact, is connected to an operating mechanism and is mounted sliding between a closed position of the contacts enabling the current to flow and a position wherein the contacts are separated and form an electric arc between them, and a means for producing an axial magnetic field in the are formation zone. This cartridge comprises at least one conducting shield (11) fitted around the periphery of at least one of the contacts (3,4), said shield (11) being shaped and arranged in such a way as to withstand the electric field arising from the recovery voltage imposed by the power system after breaking and to thus considerably reduce the electric field at the edge of said contact (3,4).
Full Text

VACUUM CARTRIDGE FOR AN ELECTRICAL PROTECTION APPARATUS SUCH AS A SWITCH OR CIRCUIT BREAKER.
Background of the invention
The present invention relates to a vacuum cartridge for an electrical protection apparatus such as a switch or a circuit breaker, said cartridge comprising an enclosure of substantially cylindrical shape closed by two end plates, two contacts extending axially inside the enclosure, at least one whereof, called the movable contact, is connected to an operating mechanism and is mounted sliding between a closed position of the contacts enabling the current to flow and a position wherein the contacts are separated and form an electric arc between them, and a means for producing an axial magnetic field in the arc formation zone. A vacuum circuit breaker of the above-mentioned kind is described in the document FR 2,682,808 or FR 2,726,396 filed by the applicant.
In this type of circuit breaker, the vacuum cartridges have under strong currents a breaking capacity which is limited by the following phenomenon. When the current flows, the arc moves liquid matter coming from the melting contact to the edge of the contacts. This very hot liquid matter (about 2000°) is situated at the edge of the contacts at the moment breaking occurs. After breaking, the recovery voltage imposed by the power system is established between the two contacts. On account of the geometric shape of the contacts, the electric field generated by this voltage is maximum at the edges of the contacts. This gives rise to the following undesirable phenomena. Firstly, when cooling, the liquid continuously gives off metallic vapors and gases. These emissions create an atmosphere

with a high gas density which, in an environment normally in a strong vacuum, has a reduced dielectric strength. Secondly, the electric field, present just above the liquefied and very hot matter, gives rise to emission of electrons by a thermo-electric mechanism. These free electrons ionize the vapor and the gas. The combination of these two phenomena then leads to rearcings and to failure of the cartridge in breaking. In addition, the electric field is liable to deform the surface of the liquid increasing the electric field even fiirther. This is a detrimental phenomenon that is self-amplifying and that can lead to rearcing. To overcome these drawbacks in industrialized cartridges, certain measures have been taken that consist in respecting a distance, called the optimal distance, between the contacts and the wall of the enclosure, which distance guarantees a maximum breaking capacity. This therefore imposes constraints as to the volume of the cartridge. Furthermore, some of the cartridges of the kind referred to above, as described in the document FR 2,726,396, in addifion comprise a metal shield acting as the wall of the enclosure. This shield is connected to one of the contacts, more often than not to the stationary contact, and secondarily produces an increase of the electric field created at the level of the movable contact. Thus, dielectrically, the cartridge is considered as being asymmetric. The electric field is stronger at the edges of the movable contact than at the edges of the stationary contact. And, depending on the polarity of the recovery voltage, the dielectric strength after breaking is more or less good. Thus it is preferable for it to be the stationary contact that is subjected to a negative voltage rather than the movable contact. When the movable contact is subjected to a negative voltage with respect to the stationary contact, the hot matter emits more electrons due to the presence of the stronger electric field, which increases the risks of rearcing. This asymmetry in terms of geometry is also

expressed by an asymmetry in terms of breaking capacity, the difference being about 15% for a rated current of 25kA rms.
Summary of the invention
The present invention overcomes these problems and proposes a vacuum cartridge with improved breaking capacity and whose behavior on breaking is more symmetric. The cartridge achieved according to the invention can also be reduced in size.
For this purpose, the object of the present invention is to achieve a vacuum cartridge of the previously mentioned kind, this cartridge being characterized in that it comprises at least one conducting shield fitted around the periphery of at least one of the contacts, said shield being shaped and arranged in such a way as to withstand the electric field arising from the recovery voltage imposed by the power system after breaking and to thus considerably reduce the electric field at the edge of the contact.
According to a particular embodiment, the above-mentioned shield is electrically connected to said contact and is sufficiently separated from said contact for the liquid running on the contact surfaqe of said contact not to be able to reach said shield. For this purpose, a trench separates the contact surface of the contact from the edge of said shield.
According to a particular feature, the above-mentioned shield is present around the whole of said contact.

According to another feature, the above-mentioned shield presents a semi-annular shape and is fixed onto the bottom part of the movable contact.
According to another feature, the cartridge comprises, for one or each contact, a shield called the first shield comprising the features mentioned above taken either alone or in combination, and a shield called the second shield, fitted between the shield called the first shield and the enclosure of the cartridge, said second shield being designed to protect the enclosure fi'om metallization by the arc vapor and secondarily producing an increase of the value of the electric field on said contact.
According to a particular feature, the physical continuity is achieved on the contacts in the closed position at a place where the wear of the contacts is minimal.
According to a particular feature, the physical continuity is achieved by means of a ring, sectors of ring or studs arranged on the contact surface of one of the contacts and situated respectively facing a ring, sectors of ring or studs arranged on the contact surface of the other of the contacts.
According to a particular feature, these rings, sectors of ring or studs are situated above the above-mentioned trench(es) separating the shield(s) called the first shield(s) firom the associated contact(s).
Brief description of the drawings

But other advantages and features of the invention will become more clearly apparent from the following detailed description which refers to the accompanying drawings given for example purposes only and in which:
- Figure 1 is an axial sectional view of a vacuum cartridge according to the prior art,
- Figure 2 is a perspective view of a vacuum cartridge according to the invention,
- Figure 3 is an axial sectional view of the vacuum cartridge according to the invention of the previous figure,
- Figure 4 is an axial sectional view of a cartridge according to the invention of symmetric type,
- Figure 5 is an axial sectional view of a cartridge according to the invention, the contacts being in addition equipped with inclined slits,
- Figure 6 is an axial sectional view of a cartridge according to the invention, with slits and rings,
- Figure 7 is a graph illustrating the relation between the breaking capacity and the distance between the contacts and the wall, for a cartridge according to the prior art and a cartridge according to the invention,
- Figure 8 is a graphic representation illustrating the relation between the breaking capacity and the diameter of the contacts for a cartridge according to the prior art and a cartridge according to the invention, and
- Figure 9 is an axial sectional view of another embodiment of a vacuum cartridge
according to the invention.
Detailed description of a preferred embodiment

In figures 1 to 6, a vacuum cartridge A can be seen designed in particular to be incorporated in a medium voltage electric circuit breaker to perform breaking of an electric circuit in case of a fault occurring or of a deliberate opening order of the electric circuit. In figure 1, a vacuum cartridge A according to the prior art can be seen. This vacuum cartridge A comprises a cylindrical enclosure E closed off by two end plates 1,2 inside which there are housed two arcing contacts 3,4, respectively a stationary arcing contact 3 and a movable arcing contact 4. This movable contact 4 is mechanically connected by means of an actuating rod 5 to an operating device (not represented), said rod 5 being connected to said device via one 5a of its ends and being fixedly secured to the movable arcing contact 4 via its opposite end 5b. This operating device is able to move the above-mentioned rod 5 and the movable contact 4 in translation inside the enclosure E between two positions respectively a closed position of the contacts corresponding to normal operation of the apparatus and an open or separated position of the contacts after a fault has occurred in the electric circuit to be protected or when a deliberate opening order of the electric circuit has been made. It can also be seen that an internal winding 6,7 is fitted to the rear of each of the contacts 3,4, said windings 6,7 constituting a means of producing an axial magnetic field capable of performing diffusion of the arc created between the contacts after the contacts have separated when breaking takes place. It can also be seen that a metallic shield 9 is fitted around the end 5b of the actuating rod 5 connected to the movable contact 4, said shield 9 and a part of another shield 1 being situated around the movable contact 4 and producing an increase of the electric field created at the level of the movable contact during breaking.
In figures 2 and 3, a vacuum cartridge A according to the invention can be seen comprising in addition to the elements mentioned above, a shield 11 designed to reduce the electric

field at the edges of the contact 4. This shield 11, of semi-annular shape, is arranged around the whole periphery of the movable contact 4 and presents two circular edges 11 a, lib of different diameters. This shield 11 is electrically connected to the movable arcing contact 4 by its bottom circular edge lib and is sufficiently separated from said contact 4 for the liquid, flowing over the contact surface under the pressure of the arc, not to be able to reach said shield 11. A trench 14 is thus created between the contact 4 and the shield 11, said trench 14 having a depth of 5 mm and a width comprised between 0.5 and 4 mm. The shape of the shield 11 is such that the value of the electric field at the edges of the contact 4 is substanfially reduced. Thus, the edge 1 la of said shield 11 is flush with the contact pad or is at a slightly smaller height than that of the contact pad, the difference being comprised between 0 and 5 mm when the shield 11 is slightly set back with respect to the contact 4. The shield 11 has to present a good thermal resistance, as projections of drops coming fi-om the contact 4 can make it undergo thermal shocks. Thus, the shield 11 is preferably made of copper or of the same material as the contact 4. Altematively, this shield 11 can be made of a refi'actory material such as SiC, except for the insulators. The breaking capacity of the cartridge A of this figure is 20% greater than that of figure 1. The protective shield 11 according to the invention substantially reduces the distance between the movable contact 4 and the metal enclosure E. Thus, despite the fact that the shield 11 reduces this distance substantially, a considerable increase of the breaking capacity is obtained as indicated by the curve 2 in figure 7, whereas curve 1 represents the behavior of a cartridge of the prior art. This curve in fact represents the breaking capacity P in percentage on the y-axis, and the distance 1 of the shield with respect to the wall in mm on the x-axis. In this embodiment, due to the shield 11, the distance between the movable contact 4 and the wall of the enclosure E has been reduced and is now 9 mm whereas it was initially 13 mm. The

shield 11 therefore presents a very high electric field which is not detrimental to the
breaking capacity.
Preferably, the shield 11 is arranged around the movable contact 4, as illustrated in figures
2,3, but another shield can also be placed, in addition to the first one, around the stationary
contact 3.
This shield 11 can also be advantageously used in cartridges of the symmetric type with a
floating shield as illustrated in figure 4. This cartridge in fact presents, for each of the
contacts 3,4, an intemal winding 6,7 situated behind the contact 3,4, a metallic shield 8,9
here in the form of a cup extending close to the wall of the enclosure, between the intemal
winding 6,7 and the enclosure, and two shields 10,11 according to the invention arranged
respectively around the stationary contact 3 and around the movable contact 4.
In figure 5, the invention is put into application in a cartridge A wherein the contacts are
equipped with slits 12 as described in French Patent application FR 2,808,617. These slits
12 are made in the contacts 3,4 so as to receive and facilitate flow of the contact liquid in
the direction of the surfaces situated under the contact surfaces, the liquid coming from
melting of the contact material due to the concentration effect of the arc during breaking.
These slits 12 enable the contact surface between the arcing contacts 3,4 and the liquid to
be increased so as to create surfaces hidden for the arc but accessible for the liquid. This
arrangement has the effect of speeding up cooling of said contact material in spite of the
concentration of the arc during breaking.
Due to these arrangements, more time elapses before the liquid reaches the edges of the
contacts 3a,4a. Thus, the liquid reaches the edges of the contacts 3a,4a at a time when the
current values are very high.

In the embodiment described in this figure, the movable contact 4 is equipped with a shield 11 according to the invention. The advantageous effects associated with the shield 11 which surrounds the contact 4 are enhanced by the presence of the slits 12 in the contacts 3,4, since the liquid on the one hand doesn*t reach the shield 11, and in addition takes longer to reach the edges of the contacts 3a,4a.
In figure 6, a cartridge A can be seen comprising an external winding 17 and comprising in addition two rings 15,16 enabling the physical continuity between the two contacts 3,4 to be achieved in the closed position.
The contacts 3,4 of the cartridge A of the previous figure present greater wear than standard cartridges for the following reasons - the liquid created when breaking takes place doesn^t stagnate at the surface, and the increase in breaking capacity makes this erosion increase even more. It is then advantageous to separate the place where physical continuity in the closed position of the contacts 3,4 enabling current conduction is achieved from the location on the contacts presenting maximum wear. It is however known that the axial magnetic field created by the extemal and internal windings stabilizes the arc well and rather tends to displace it to where it is strongest, at least for strong currents. It is at these places that the erosion will be the greatest. It is then advantageous to achieve the physical continuity elsewhere. This physical continuity can be achieved by means of several parts able to take the form of a ring 15,16. For this purpose, the cartridge described in this figure comprises, at the level of each of the contacts 3,4, a ring 15,16 placed above the trench 13,14 separating the shield 10,11 and the contact 3,4. Due to this arrangement, the liquid can flow freely through the slits 12. In this embodiment, the breaking capacity is increased, the value of this increase being able to reach 60% of the breaking capacity associated to a cartridge according to figure 1.

It should be noted that this physical continuity can also be achieved with rings having a smaller diameter that are no longer in contact with the shield. This physical continuity can also be achieved by means of studs or sectors of rings.
It should also be noted that the shield could be of another shape than semi-annular, for example rectangular etc...
In figure 9, the shield is also used for conducting a part of the current. When a part of the current passes through the shield, the current can be given a direction of rotation in order that the axial field be increased. This rotation of the current can be obtained by means of inclined slits provided in the shield.
In this figure, it can be seen that the inclination of the slits in the coil constituted by the shield is opposed to the inclination of the slits in the contact. The first ones act to produce the axial magnetic field whereas the second ones act to allow the liquid (melted metal) to flow. Then, due to these different inclinations, the liquid flowing on the contact is thrown against the massive part of the shield ; then, the slits in the shield do not allow the passage of the liquid. The shield with the slits fulfils three functions which are respectively, to avoid the throwing of liquid metal, to mechanically support the contact ring and the current conductor, and to increase or create the axial magnetic field between the contacts. The invention could also advantageously be put into application in a cartridge as described in the Patent FR 2,745,118. In this embodiment of the cartridge not illustrated in the drawings, said cartridge in addition comprises another shield made of conducting material and electrically connected to one of the contacts, said shield being situated inside the enclosure facing the gap separating the contacts and located around the contacts at a preset position according to the position of the current inputs so that when the arc tends to deviate from the above-mentioned gap, this arc places itself between the contacts and the shield.

The switch of this embodiment presents an improved breaking capacity, this breaking capacity being able to be obtained by producing a smaller magnetic field the continuous current-carrying capacity whereof is increased.
Using a shield according to the invention in such a switch enables the breaking capacity to be further increased.
Figure 8 illustrates the relation between the breaking capacity c and the diameter of the contacts d for a cartridge according to the invention and for a cartridge according to the prior art. The current c in kA rms is represented on the y-axis, whereas the diameter d of the contacts in mm is represented on the x-axis. In this figure, the points represented by squares represent values obtained with a conventional cartridge comprising an external winding (12kV). The points represented by triangles represent values obtained with a cartridge comprising an internal winding (24kV). The circles correspond to shown values. The dark line represents the limit for a cartridge of conventional type using an axial field whereas the light line represents the limit for a cartridge according to the invention. It can thus be seen on this curve that the values of the breaking capacity for the same contact diameter are greater in the case of a cartridge according to the invention than those concerning a cartridge according to the prior art. This results in the same breaking capacity value being able to be obtained with a contact diameter value reduced by one third. Furthermore, the cartridge according to the invention presents a more symmetric behavior on breaking, in particular when the cartridge is of the type comprising slits. Thus, the dielectric strength after breaking hardly varies at all with the polarity of the recovery voltage.

Naturally, the invention is not limited to the embodiments described and illustrated which have been given for example purposes only.
On the contrary, the invention encompasses all the technical equivalents of the means described and combinations thereof if these are performed according to the spirit thereof




CLAIMS
1. Vacuum cartridge for an electrical protection apparatus such as a switch or a circuit breaker, said cartridge comprising an enclosure of substantially cylindrical shape closed by two end plates, two contacts extending axially inside the enclosure, at least one whereof, called the movable contact, is connected to an operating mechanism and is mounted sliding between a closed position of the contacts enabling the current to flow and a position wherein the contacts are separated and form an electric arc between them, and a means for producing an axial magnetic field in the arc formation zone, characterized in that it comprises at least one conducting shield (11) fitted around the periphery of at least one of the contacts (3,4), said shield (11) being shaped and arranged in such a way as to withstand the electric field arising from the recovery voltage imposed by the power system after breaking and to thus considerably reduce the electric field at the edge of said contact (3,4), and in that the physical continuity on the contacts (3,4) in the closed position is achieved by means of a ring (15), sectors of ring or studs arranged on the contact surface of one (3) of the contacts and situated respectively facing a ring (16), sectors of ring or studs arranged on the contact surface of the other (4) of the contacts.
2. Vacuum cartridge according to claim 1, characterized in that the above-mentioned shield (11) is used for conducting at least a part of the current.

3. Vacuum cartridge according to claim 2, characterized in that said shield (11) comprises slits arranged in such a way that said shield (11) constitutes a coil.
4. Vacuum cartridge according to any one of claims 1 to 3, characterized in that the above-mentioned shield (11) is electrically connected to said contact (3,4) and is sufficiently separated from said contact for the liquid running on the contact surface of said contact (3,4) not to be able to reach said shield (11).
5. Vacuum cartridge according to any one of claims 1 to 4, characterized in that the above-mentioned shield (11) is present around the whole of said contact (3,4).
6. Vacuum cartridge according to any one of the foregoing claims, characterized in that the shield (11) is shaped in such a way as to create a trench (14) presenting a width comprised between 0.5 mm and 4 mm between said shield (11) and said contact (3,4).
7. Vacuum cartridge according to claim 6, characterized in that the above-mentioned trench (14) presents a depth of about 5 mm.
8. Vacuum cartridge according to any one of the foregoing claims, characterized in that the edge (11a) of the above-mentioned shield (11) is substantially at the same level as the contact pad (3,4), or is of a slightly smaller height than the height of this contact pad (3,4).

9. Vacuum cartridge according to any one of the foregoing claims, characterized in that the above-mentioned shield (11) presents a semi-annular shape and is fixed onto the bottom part of the movable contact (3,4).
10. Vacuum cartridge according to any one of the foregoing claims, characterized in that the shield (11) is made of the same material as the contact (3,4), for example copper.
11. Vacuum cartridge according to any one of the foregoing claims, characterized in that the shield (11) is made of a refractory material such as SiC.
12. Vacuum cartridge according to any one of the foregoing claims, characterized in that the above-mentioned shield (11) is fitted around the movable contact (4).
13. Vacuum cartridge according to any one of the foregoing claims, characterized in that it comprises another shield (8,9,1), said second shield (8,9) being designed to protect the enclosure from metallization by the arc vapor and secondarily producing an increase of the value of the electric field on said contact (3,4).
14. Vacuum cartridge according to claim 13, characterized in that said second shield (8,9) is fitted between the shield (10,11) called the first shield and the enclosure E of the cartridge A.
15. Vacuum cartridge according to any one of the foregoing claims, characterized in that the or each contact (3,4) comprises at least one slit (12) passing through said contact

(3,4), said slits (12) being arranged in such a way as to receive the above-mentioned liquid and to facilitate its flow (3,4).
16. Vacuum cartridge according to claims 1 and 16, characterized in that these rings (15,16), sectors of ring or studs are situated above the above-mentioned trench(es) (13,14) separating the shield(s) called the first shield(s) (10,11) from the associated contact(s) (3,4).
17. Vacuum cartridge according to any one of the foregoing claims, characterized in that it comprises a shield called the third shield, made of conducting material, said shield being situated inside the enclosure E facing the gap separating the contacts (3,4) and being electrically connected to one of the contacts (3,4), said shield being located around the contacts (3,4) in a preset position according to the position of the current inputs so that when the arc tends to deviate fi-om the above-mentioned gap, this arc places itself between the contacts (3,4) and the shield.
18. Vacuum cartridge according to claim 13, characterized in that the inclination of the slits in the contacts is opposed to the inclination of the slits (18) in the shield (11) so that the liquid flowing through the slits of the contacts cannot flow through the slits of the shield (11).

19. A vacuum cartridge substantially as herein described with reference to the accompanying drawings.


Documents:

521-CHE-2003 AMENDED CLAIMS 18-06-2010.pdf

521-CHE-2003 CORRESPONDENCE OTHERS 18-06-2010.pdf

521-che-2003 form-3 18-06-2010.pdf

521-CHE-2003 OTHER PATENT DOCUMENT 18-06-2010.pdf

521-CHE-2003 EXAMINATION REPORT REPLY RECIEVED-19-08-2009.pdf

521-CHE-2003 OTHERS-19-08-2009.pdf

521-che-2003-abstract.pdf

521-che-2003-claims.pdf

521-che-2003-correspondnece-others.pdf

521-che-2003-description(complete).pdf

521-che-2003-drawings.pdf

521-che-2003-form 1.pdf

521-che-2003-form 26.pdf

521-che-2003-form 3.pdf

521-che-2003-form 5.pdf


Patent Number 241822
Indian Patent Application Number 521/CHE/2003
PG Journal Number 31/2010
Publication Date 30-Jul-2010
Grant Date 27-Jul-2010
Date of Filing 25-Jun-2003
Name of Patentee SCHNEIDER ELECTRIC INDUSTRIES SAS
Applicant Address BOUVELARD FRNKIN ROOSEVELT, F-92500 RUEIL MALMAISON, FRANCE.
Inventors:
# Inventor's Name Inventor's Address
1 OLIVE Serge LE GRAND CHAMP, 38760 SAINT PAUL DE VARCES, FRANCE.
2 SCHELLEKENS Hans IMPASSE DE LA SOIE, 38660 LA TRASSE
PCT International Classification Number H01H9/02
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 0208033 2002-06-27 France