Electrical switching device with a triple motion contact arrangement

Abstract

A contact arrangement has a longitudinal axis and includes a first contact group with a first contact and a second contact and a second contact group with a third contact and a fourth contact. The first contact interacts electrically and mechanically with the third contact, and/or the second contact interacts electrically and mechanically with the fourth contact, for closing and opening the contact arrangement. At least one mechanical coupling is provided for transmitting an actuation force to the second contact group and thereby moving the second contact group. The at least one mechanical coupling is adapted to move the third and the fourth contact in such a way that their speeds differ along at least a portion of a travel path of the third contact or along at least a portion of a travel path of the fourth contact.

Claims

1. A contact arrangement having a longitudinal axis and comprising: a first contact group with a first contact and a second contact and a second contact group with a third contact and a fourth contact, the first contact interacting electrically and mechanically with the third contact and/or the second contact interacting electrically and mechanically with the fourth contact, for closing and opening the contact arrangement, the first contact and the second contact configured to have a same speed, at least one mechanical coupling configured to transmit an actuation force to the second contact group and thereby move the second contact group, the at least one mechanical coupling configured to move the third contact and the fourth contact in such a way that speeds of the third contact and the fourth contact differ along at least a portion of a travel path of the third contact or along at least a portion of a travel path of the fourth contact, wherein the at least one mechanical coupling is a linkage having a first kinematic chain and a second kinematic chain, wherein the first kinematic chain is movably connected to the first contact group in an electrically insulating manner and the second kinematic chain is movably connected to the second contact group, and wherein the first kinematic chain has at least two levers, with a first lever of the first kinematic chain rotationally connected to a bearing and fixedly connected to a first lever of the second kinematic chain, and with an end lever of the first kinematic chain movably connected to the first contact group.

2. The contact arrangement according to claim 1, wherein the first contact and the third contact are nominal contacts, and/or the second contact and the fourth contact are arcing contacts; and/or the first contact group is on one side of an arcing zone of a circuit breaker and the second contact group is on an opposite side of the arcing zone, when seen along the longitudinal axis.

3. The contact arrangement device according to claim 1, wherein the first kinematic chain is movably connected to the first contact group by an intermediary member, and wherein the intermediary member is linearly movable parallel to the longitudinal axis by a mechanical force.

4. The contact arrangement according to claim 3, wherein the first lever of the first kinematic chain and the end lever of the first kinematic chain are connected by a common joint; and/or wherein the connecting rod is attached to the end lever of the first kinematic chain by an end joint.

5. The contact arrangement device according to claim 3, wherein the mechanical force is exerted on the intermediary member by a movable insulating nozzle of the first contact group.

6. The contact arrangement according to claim 4, wherein the common joint connecting the first lever with the second lever of the first kinematic chain performs a rotational movement around the bearing; and/or the common joint connecting the first lever with the second lever of the second kinematic chain performs a rotational movement around the bearing; and/or the end joints perform a linear movement parallel to the longitudinal axis; and/or a joint connecting the bearing with the first lever of the first kinematic chain is stationary and only allows a rotational movement of the first lever of the first kinematic chain; and/or a joint connecting the bearing with the first lever of the second kinematic chain is stationary and only allows a rotational movement of the first lever of the second kinematic chain.

7. The contact arrangement according to claim 1, wherein the second kinematic chain has at least two levers, the first lever of the second kinematic chain rotationally connected to the bearing and fixedly connected to the first lever of the first kinematic chain, and an end lever of the second kinematic chain movably connected to the second contact group.

8. The contact arrangement according to claim 7, wherein the first lever and the end lever of the second kinematic chain are connected by a common joint, and/or wherein the end lever of the second kinematic chain is pivotably attached by an end joint to the second contact group.

9. The contact arrangement according to claim 7, wherein the at least one mechanical coupling comprises a first linkage and a second linkage, and the end levers of the first kinematic chain of each one of the linkages are pivotably connected by end joints to the first contact group in such a way that they are moved by the first contact group simultaneously; and wherein the end joints of the end levers of the first kinematic chains perform a linear movement parallel to the longitudinal axis.

10. The contact arrangement according to claim 9, wherein an end lever of the second kinematic chain of the first linkage is pivotably connected by an end joint to the fourth contact, and/or an end lever of the second kinematic chain of the second linkage is pivotably connected by an end joint to the third contact; wherein the end joints of the end levers of the second kinematic chains perform a linear movement parallel to the longitudinal axis.

11. The contact arrangement according to claim 9, wherein a transmission ratio between the first kinematic chain and the second kinematic chain of the first linkage is not equal to a transmission ratio between the first kinematic chain and the second kinematic chain of the second linkage.

12. The contact arrangement according to claim 1, wherein the at least one mechanical coupling comprises one linkage and the second kinematic chain of the one linkage comprises two end levers, of which a first end lever is pivotably connected at one end by an end joint to the third contact and a second end lever is pivotably connected at one end by an end joint to the fourth contact.

13. The contact arrangement according to claim 12, wherein each end lever of the second kinematic chain is pivotably connected to a neighbouring lever of the second kinematic chain by a distinct joint.

14. The contact arrangement according to claim 12, wherein the two end levers of the second kinematic chain are connected to a neighbouring lever of the second kinematic chain by a common joint.

15. The contact arrangement according to claim 14, wherein the common joint connects one of the end levers of the second kinematic chain pivotably with the fourth contact, and the other end lever of the second kinematic chain is connected fixedly to the third contact and comprises a guide rail guiding the common joint.

16. The contact arrangement according to claim 15, wherein a difference between a transmission ratio of the first kinematic chain with one branch of the second kinematic chain and a transmission ratio of the first kinematic chain with another branch of the second kinematic chain is given by a shape of the guide rail.

17. The contact arrangement according to claim 16, wherein the difference is given by a steepness of sides of the guide rail relative to the longitudinal axis.

18. The contact arrangement according to claim 12, wherein a transmission ratio between the first kinematic chain and the second kinematic chain with one of the end levers is not equal to a transmission ratio between the first kinematic chain and the second kinematic chain with another of the end levers.

19. The contact arrangement according to claim 1, wherein the mechanical coupling is configured such that a predefined time period between touching or separation of the first contact and third contact and touching or separation of the second contact and the fourth contact is not exceeded.

20. The contact arrangement according to claim 1, wherein the mechanical coupling is configured such that the fourth contact is moved faster than the third contact, and/or that the travel path of the fourth contact is longer than the travel path of the third contact.

21. The contact arrangement according to claim 1, wherein the mechanical coupling is configured such that the speed of the third contact and/or the speed of the fourth contact is non-linear as a function of time.

22. The contact arrangement according to claim 21, wherein the mechanical coupling is configured such that the speed of the third contact is a first non-linear function of time and the speed of the fourth contact is a second non-linear function of time; and wherein the first and second non-linear functions are different.

23. The contact arrangement according to claim 1, wherein the third contact is provided with a guiding element for guiding the third contact along a linear path during the closing and the opening of the contact arrangement, and/or the fourth contact is provided with a guiding element for guiding the fourth contact along a linear path during the closing and the opening of the contact arrangement.

24. An electrical switching device comprising a contact arrangement according to claim 1, wherein the first contact group is movable along the longitudinal axis to close and open said electrical switching device.

25. The electrical switching device according to claim 24, the electrical switching device configured as an earthing device, a fast-acting earthing device, a circuit breaker, a generator circuit breaker, a switch disconnector, a combined disconnector and earthing switch, or a load break switch.

26. The electrical switching device according to claim 24, wherein the electrical switching device includes a dielectric insulation gas that comprises an organofluorine compound selected from the group consisting of: a fluoroether, an oxirane, a fluoroamine, a fluoroketone, a fluoroolefin; and mixtures and/or decomposition products thereof.

27. An electrical switching device comprising a contact arrangement having a longitudinal axis and comprising: a first contact group with a first contact and a second contact and a second contact group with a third contact and a fourth contact, the first contact interacting electrically and mechanically with the third contact and/or the second contact interacting electrically and mechanically with the fourth contact, for closing and opening the contact arrangement, the first contact group is on one side of an arcing zone of a circuit breaker and the second contact group is on the other side of the arcing zone, when seen along the longitudinal axis, at least one mechanical coupling configured to transmit an actuation force to the second contact group and thereby move the second contact group, the at least one mechanical coupling configured to move the third contact and the fourth contact in such a way that speeds of the third contact and the fourth contact differ along at least a portion of a travel path of the third contact or along at least a portion of a travel path of the fourth contact, wherein the at least one mechanical coupling is a linkage having a first kinematic chain and a second kinematic chain, wherein the second kinematic chain is movably connected to the second contact group, and wherein the first kinematic chain has at least two levers, with a first lever of the first kinematic chain rotationally connected to a bearing and fixedly connected to a first lever of the second kinematic chain, and with an end lever of the first kinematic chain movably connected to an actuator of the electrical switching device for providing the actuation force transmitted to the second contact group by the mechanical coupling of the contact arrangement according to a predefined transmission ratio and/or speed curve.

28. A contact arrangement having a longitudinal axis and comprising: a first contact group with a first contact and a second contact, and a second contact group with a third contact and a fourth contact; the first contact interacting electrically and mechanically with the third contact and/or the second contact interacting electrically and mechanically with the fourth contact, for closing and opening the contact arrangement; at least one mechanical coupling configured to transmit an actuation force to the second contact group and thereby move the second contact group; the at least one mechanical coupling configured to move the third contact and the fourth contact in such a way that speeds of the third contact and the fourth contact differ along at least a portion of a travel path of the third contact or along at least a portion of a travel path of the fourth contact; wherein the at least one mechanical coupling is a linkage having a first kinematic chain and a second kinematic chain, wherein the first kinematic chain is movably connected to the first contact group in an electrically insulating manner and the second kinematic chain is movably connected to the second contact group; wherein the first kinematic chain has at least two levers, with a first lever of the first kinematic chain rotationally connected to a bearing and fixedly connected to a first lever of the second kinematic chain, and with an end lever of the first kinematic chain movably connected to the first contact group; wherein the second kinematic chain has at least two levers, the first lever of the second kinematic chain rotationally connected to the bearing and fixedly connected to the first lever of the first kinematic chain, and an end lever of the second kinematic chain movably connected to the second contact group; wherein the at least one mechanical coupling comprises a first linkage and a second linkage, and the end levers of the first kinematic chain of each one of the linkages are pivotably connected by end joints to the first contact group in such a way that they are moved by the first contact group simultaneously; and wherein the end joints of the end levers of the first kinematic chains perform a linear movement parallel to the longitudinal axis.

29. The contact arrangement according to claim 28, wherein an end lever of the second kinematic chain of the first linkage is pivotably connected by an end joint to the fourth contact, and/or an end lever of the second kinematic chain of the second linkage is pivotably connected by an end joint to the third contact; wherein the end joints of the end levers of the second kinematic chains perform a linear movement parallel to the longitudinal axis.

30. The contact arrangement according to claim 28, wherein a transmission ratio between the first kinematic chain and the second kinematic chain of the first linkage is not equal to a transmission ratio between the first kinematic chain and the second kinematic chain of the second linkage.

31. A contact arrangement having a longitudinal axis and comprising: a first contact group with a first contact and a second contact, and a second contact group with a third contact and a fourth contact; the first contact interacting electrically and mechanically with the third contact and/or the second contact interacting electrically and mechanically with the fourth contact, for closing and opening the contact arrangement; at least one mechanical coupling configured to transmit an actuation force to the second contact group and thereby move the second contact group; the at least one mechanical coupling configured to move the third contact and the fourth contact in such a way that speeds of the third contact and the fourth contact differ along at least a portion of a travel path of the third contact or along at least a portion of a travel path of the fourth contact; wherein the at least one mechanical coupling is a linkage having a first kinematic chain and a second kinematic chain, wherein the first kinematic chain is movably connected to the first contact group in an electrically insulating manner and the second kinematic chain is movably connected to the second contact group; wherein the first kinematic chain has at least two levers, with a first lever of the first kinematic chain rotationally connected to a bearing and fixedly connected to a first lever of the second kinematic chain, and with an end lever of the first kinematic chain movably connected to the first contact group; wherein the at least one mechanical coupling comprises one linkage and the second kinematic chain of the one linkage comprises two end levers, of which a first end lever is pivotably connected at one end by an end joint to the third contact and a second end lever is pivotably connected at one end by an end joint to the fourth contact; wherein the two end levers of the second kinematic chain are connected to a neighbouring lever of the second kinematic chain by a common joint; wherein the common joint connects one of the end levers of the second kinematic chain pivotably with the fourth contact, and the other end lever of the second kinematic chain is connected fixedly to the third contact and comprises a guide rail guiding the common joint; and wherein a difference between a transmission ratio of the first kinematic chain with one branch of the second kinematic chain and a transmission ratio of the first kinematic chain with another branch of the second kinematic chain is given by a shape of the guide rail.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments, advantages and applications of the invention result from the now following description and by means of the figures. It is shown in:

(2) FIG. 1 is a sectional side view of an embodiment of a high voltage circuit breaker with a mechanical coupling;

(3) FIG. 2 is a detail sectional side view of the contacts of the circuit breaker of FIG. 1 with a contact arrangement according to the prior art;

(4) FIGS. 3, 4 and 5 are each detailed sectional side views of the contacts of the circuit breaker of FIG. 1 for a first, second and third embodiment, respectively, of a contact arrangement according to the invention; and

(5) FIG. 6 is a diagram showing curves of a travel path over time of the contacts of the circuit breaker according to FIG. 1 with mechanical couplings according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The invention is described for the example of a high voltage circuit breaker, but the principles described in the following also apply for the usage of the invention in other switching devices, e.g. of the type mentioned at the beginning.

(7) In the following, same reference numerals denote structurally or functionally same or similar elements of the various embodiments of the invention.

(8) FIG. 1 shows exemplarily a sectional side view of an embodiment of a high voltage circuit breaker 1 during an opening process, with a mechanical coupling 2. The circuit breaker 1 without the mechanical coupling 2 is rotationally symmetric about a longitudinal axis z. Only the elements of the circuit breaker 1 which are related to the present invention will be described in the following, other elements present in the figures are not relevant for understanding the invention and are known by the skilled person in high voltage electrical engineering. The first contact is typically a first nominal contact 3a and the second contact is a first arcing contact 4a, both of them belonging to the first contact group. Accordingly, the third contact is a second nominal contact 3b and the fourth contact is a second arcing contact 4b.

(9) The circuit breaker 1 is enclosed by a shell or enclosure 5 which is normally or substantially cylindrical and arranged around the longitudinal axis z. The first nominal contact 3a comprises a plurality of contact fingers, of which only two are shown here for reasons of clarity. The nominal contact fingers are formed as a finger cage around the longitudinal axis z. The second mating nominal contact 3b normally is a tube or metal tube. A shielding 5a can be arranged around the first and the second nominal contact 3a, 3b, and the first and the second arcing contact 4a, 4b. Analogue to the first nominal contact 3a also the first arcing contact 4a comprises multiple fingers arranged in a finger cage. The second arcing contact 4b is normally rod-shaped.

(10) The first contact group 3a, 4a is movable relatively to the second contact group 3b, 4b from a closed configuration, in which the respective contacts of the groups are in electrical contact to one another, info an opened configuration shown in FIG. 1, in which they are apart from one another, and vice versa. It is also possible that only the second contact group 3b, 4b moves parallel to the longitudinal axis z and the first contact group 3a, 4a is stationary. For the explanatory purposes of the present invention the first alternative is assumed. However, the invention is not limited to this configuration.

(11) An opened configuration as used herein means that the nominal contacts 3a, 3b and/or the arcing contacts 4a, 4b of the circuit breaker 1 are opened. Accordingly, a closed configuration as used herein means that the nominal contacts 3a, 3b and/or the arcing contacts 4a, 4b of the circuit breaker 1 are closed. In particular, opened configuration and closed configuration relate to end positions of the nominal contacts 3a, 3b and/or arcing contacts 4a, 4b.

(12) As mentioned the circuit breaker 1 is shown during an opening process of the electrical switching device 1 with an electric arc 3 between the arcing contacts 4a, 4b. This type of circuit breaker is known and will only be described in more detail here with respect to the actuation of the second contact group 3b, 4b and particularly with respect to the transmission of an actuation force to the second contact group 3b, 4b by the mechanical coupling 2.

(13) FIG. 2 shows a detail sectional side view of the contact arrangement of the circuit breaker 1, which is according to the prior art a full double motion interrupter.

(14) The circuit breaker 1 is shown during a closing process in this figure, in an instant when the second arcing contact 4b has already established contact to the mating arcing contact 4a. In the position of FIG. 2 (and FIG. 3-5) the nominal contacts 3a, 3b are shown in a still opened configuration. For opening the circuit breaker 1 the first contact group 3a, 4a is moved in the opposite direction of the arrow z and for dosing the circuit breaker 1 it is moved in the direction of the arrow z. These assumptions are also valid for embodiments of the invention according to FIG. 3-5.

(15) An insulating nozzle 2a is fixedly attached to the first contact group 3a, 4a. The main purpose of the insulating nozzle 2a is to control a flow of the fluid used to extinguish the electric arc 3 of FIG. 1. It is furthermore used to move an intermediary member 2b. The intermediary member may be a connecting rod 2b which is attached to a first kinematic chain 6a of a mechanical coupling s. The first kinematic chain 6a comprises a first lever 7 and a second lever 8a, which are connected by a joint 10b. The connecting rod 2b is attached to this second lever 8a by an end joint 10a. The mechanical coupling s further comprises a second kinematic chain 6b and is rotationally attached to a bearing 9 by means of a joint 10c. The second kinematic chain 6b comprises a first lever 7 and a second lever 8b, which are connected by a joint 10b. The second lever 8b is pivotably attached to the second contact group 3b, 4b by an end joint 10a. In the following the joints depicted by a circle and having the same reference numeral can be assumed to be of the same type throughout the disclosure. The joints 10a perform a linear movement parallel to the longitudinal axis z. The joints 10b connecting the first levers 7, 7 with the second levers 8a, 8b of each kinematic chain 6a, 6b respectively, perform a rotational movement around the bearing 9. The joint 10c connecting the bearing 9 with the first levers 7, 7 is stationary and only allows a rotational movement of the first levers 7, 7. It is noted that the first and the second kinematic chain 6a, 6b may have more than two levers, depending on the spatial arrangement of the mechanical coupling with respect to the second contact group 3b, 4b. For the purposes of exemplary disclosure only two levers are assumed and then the second lever is equivalent to an end lever regarding its naming. The first lever 7, 7 of one of the kinematic chains 6a, 6b is fixedly connected to the first lever 7, 7 of the other kinematic chain 6b, 6a. In other words the first levers 7, 7 may be made in one piece, with one leg belonging to the first kinematic chain 6a and the other leg belonging to the second kinematic chain 6b.

(16) As mentioned above, an end joint 10a couples the second contact group 3b, 4b to the mechanical coupling s. In the figure, the nominal contact 3b and the arcing contact 4b are shown to be connected by a bar containing the end joint 10a. This is intended for illustration purposes to emphasize a rigid mechanical connection between the contacts 3b, 4b and that they are moved simultaneously via the end joint 10a.

(17) For the purposes of this entire disclosure the term kinematic chain is interpreted as an assembly of rigid bodies movably connected by joints or other elements. The rigid bodies, or levers, are constrained by their connections to other levers. The levers for the mechanical coupling may e.g. be metal bars.

(18) In the following, the contact arrangement according to the prior art is replaced by embodiments of contact arrangements according to the invention, as triple motion interrupters, in this context triple motion refers to a motion of the first contact group 3a, 4a, a motion of the arcing contact 4b and a motion of the nominal contact 3b, whereas double motion refers to a motion of the first contact group 3a, 4a and a motion of the second contact group 3b, 4b.

(19) FIG. 3 shows a detail sectional side view of the contacts 3a, 3b, 4a, 4b of the circuit breaker 1 with a first embodiment of a contact arrangement according to the invention, in this embodiment a mechanical coupling 2 comprises a first and a second linkage 2, 2. The first linkage 2 comprises a first and a second kinematic chain 6a and 6b, each of which is formed by a first lever 7, 7 and an end lever 8a, 8b, respectively. The second linkage 2 comprises a first and a second kinematic chain 6c and 6d, each of which is formed by a first lever 7a, 7a and an end lever 8c, 8d, respectively. The first linkage 2 is attached to a bearing 9 and the second linkage 2 is attached to a bearing 9a. The end levers 8a, 8c of the first kinematic chains 6a, 6c are both connected to an intermediary member 2b. Preferably, the intermediary member 2b is a connecting rod or tube or bar 2b which is linearly movable parallel to the longitudinal axis z by a mechanical force exerted on it, for example by a moving insulating nozzle 2a connected to the first contact group 3a, 4a or otherwise by an intermediary member of any kind. The insulating nozzle 2a has been explained in connection with FIG. 2. Such an arrangement of the connecting rod 2b and the insulating nozzle 2a is also preferred for the subsequent embodiments of the invention according to FIGS. 4 and 5. By this connection type it is made sure that the second contact group 3b, 4b is not moved before the first contact group 3a, 4a is moved. This alternative can e.g. be used for circuit breakers 1 featuring two movable contact groups.

(20) The end levers 8a, 8c may also be connected to another type of actuating device (not shown) arranged within the circuit breaker 1. By this it is made sure that the second contact group 3b, 4b can be moved independently of the first contact group 3a, 4a. This alternative can e.g. be used for circuit breakers 1 featuring a fixed contact group (here the first contact group) and a movable contact group (here the second contact group).

(21) It shall be noted that the usage of an alternative actuator for the first linkage 2 and the second linkage 2 is possible for ail embodiments of the mechanical coupling 2 (e.g. of FIGS. 4 and 5) if the type of circuit breaker used requires this arrangement.

(22) In embodiments, the electrical switching device 1 comprises a contact arrangement having a longitudinal axis z and comprises a first contact group 3a, 4a with a first contact 3a and a second contact 4a and a second contact group 3b, 4b with a third contact 3b and a fourth contact 4b; wherein the first contact 3a interacts electrically and mechanically with the third contact 3b and/or the second contact 4a interacts electrically and mechanically with the fourth contact 4b for closing and opening the contact arrangement; wherein at least one mechanical coupling 2 is provided for transmitting an actuation force to the second contact group 3b, 4b and thereby moving the second contact group 3b, 4b; wherein the at least one mechanical coupling 2, 2; 2 is adapted to move the third contact 3b and the fourth contact 4b in such a way that their speeds differ along at least a portion of a travel path of the third contact 3b or along at least a portion of a travel path of the fourth contact 4b; wherein the at least one mechanical coupling is a linkage 2, 2; 2 having a first kinematic chain 6a, 6c; 6a and a second kinematic chain 6b, 6d; 6b; the second kinematic chain 6b, 6d; 6b is movably connected to the second contact group 3b, 4b; and the first kinematic chain 6a, 6c; 6a has at least two levers 7, 7a; 8a, 8c, with a first lever 7, 7a of the first kinematic chain 6a, 6c; 6a being rotationally connected to a bearing 9, 9a and being fixedly connected to a first lever 7, 7a of the second kinematic chain 6b, 6d; 6b; and an end lever 8a, 8c of the first kinematic chain 6a, 6c; 6a is moveably connected to an actuator of the electrical switching device 1 for providing the actuation force transmitted to the second contact group 3b, 4b by the mechanical coupling 2 of the contact arrangement according to a predefined transmission ratio and/or speed curve.

(23) In the following the movement of the individual moving parts of the circuit breaker 1 are explained for the case when the circuit breaker 1 is being closed, based on the double arrows 30 to 36. The opening of the circuit breaker 1 is analogous, with the double arrows pointing into the opposite direction. It shall be noted that the double arrows 31 to 34 of the first linkage 2 and of the second linkage 2 indicate in FIG. 3 a same movement of the respective element with respect to direction and distance and/or speed, whereas the double arrows 35 and 36 indicate a same movement of the respective element only with respect to direction, but not with respect to distance and/or speed. Double arrows starting inside a joint represent the movement of the joint. Double arrows arranged around a joint represent a movement of levers.

(24) In a first step the first contact group 3a, 4a is shifted along the longitudinal axis z in the direction of the arrow 30. By this, the nozzle 2a, which is fixedly attached to the first contact group 3a, 4a, and the connecting rod 2b also move in this direction. Consequently, the joints 10a of the end levers 8a, 8c of the first kinematic chains 6a, 6c of the respective linkages 2, 2 also perform a linear movement in the direction of the arrows 31. Thereby, the joints 10b connecting the end levers 8a and 8c with the respective first levers 7, 7a are pushed in the direction of the arrows 32. The respective first levers 7, 7a thereby rotate about their corresponding bearing 9, 9a (arrows 33), causing the joints 10b between the first levers 7, 7a and the end levers 8b, 8d of the corresponding second kinematic chains 6b, 6d to perform a rotation in the direction of the arrows 34. By this, the end levers 8b, 8d of the respective second kinematic chain 6b, 6d are pushed in a linear direction of the arrows 35 and 36 respectively. Each end lever 8b, 8d pushes, via the respective joints 10a, the respective contact of the second contact group 3b, 4b towards the first contact group 3a, 4a. The length or shape in general of the end levers 8b, 8d determine the shifting distance of the respective contact 3b, 4b and/or their shifting speed.

(25) As can be seen in FIG. 3 by the thicker lines 19, the third contact 3b and/or the fourth contact 4b is or are provided each with a guiding element 19 for guiding the third contact 3b and/or the fourth contact 4b, respectively, along a linear path during the closing and the opening of the contact arrangement. The provision of the guiding element or elements 19 is preferred, because it supports the respective contact against radial force components acting on it when the mechanical coupling 2 is actuated for opening or closing the contact arrangement. The following embodiments of the invention are also preferably provided with such guiding elements 19.

(26) FIG. 4 shows a detailed sectional side view of the contacts 3a, 3b, 4a, 4b of the circuit breaker 1 in a second embodiment of a contact arrangement according to the invention, in this embodiment the mechanical coupling is formed by a single linkage 2. The first kinematic chain 6a of the linkage 2 is the same as the first kinematic chains of the linkages 2, 2 of the embodiment of FIG. 3 and is also connected by an end joint 10a to a connecting rod 2b. Therefore it will not be described in more detail. The second kinematic chain 6b of the linkage 2 has a first end lever 12a which is pivotably connected to the fourth contact 4b and a second end lever 12b which is pivotably connected to the third contact 3b. The end levers 12a, 12b are connected at their other end to the first lever 7 of the second kinematic chain 6b by means of two distinct joints 10b. In this embodiment the transmission ratios between the first kinematic chain 6a and the two branches of the second kinematic chain 6b is different. The difference between the two ratios is given by the relative design and arrangement of the two branches, and in particular on the one hand by the distance between the joints 10b linking the first lever 7 of the second kinematic chain 6b with each one of the end levers 12a, 12b and on the other hand by the length difference of the two end levers 12a, 12b.

(27) The movement of the moving parts is in this embodiment analogous to the movement of one of the linkages 2, 2 of FIG. 3 and will therefore not be explained here in more detail. The double arrows again represent the movement directions during the closing process.

(28) FIG. 5 shows a detail sectional side view of the contacts 3a, 3b, 4a, 4b of the circuit breaker 1 with a third embodiment of a contact arrangement according to the invention. In the following only the differences to the embodiment of FIG. 4 are described. In this embodiment the two end levers 12a, 13 are linked to the first lever 7 of the second kinematic chain 6b by means of a common joint 10b. The first end lever 12a has an identical connection like the one in FIG. 4. The second end lever 13 comprises a guide rail 15 which guides the common joint 10b. The second end lever 13 is fixedly attached to the third contact 3b by means of a joint 14. Thus it is attached to said contact 3b in a stiff way and can therefore only perform a translation movement parallel to the longitudinal axis z. Contrary to this the common joint 10b can only perform a rotational movement around the bearing 9, being constrained by the rigid first lever 7. The result is that the third contact 3b is shifted back and forth by the constraint of the movement of the common joint 10b in the guide rail 15. When the electrical switching device 1 is being closed, the common joint 10b rotates in the direction shown by the double arrow, thus impacting a first side 15a of the guide rail 15 and gliding along it, thus forcing the corresponding end lever 13 to shift in the direction of the arrow of the joint 14. When the switching device 1 is being opened the common joint 10b rotates in the opposite direction, impacts a second side 15b of the guide rail and glides along it, thus forcing the corresponding end lever 13 to move in the direction of the arrow z. The difference between the transmission ratio of the first kinematic chain 6a with the one branch of the second kinematic chain 6b and the transmission ratio of the first kinematic chain 6a with the other branch of the second kinematic chain 6b is given by the shape of the guide rail 15. More precise, the steepness of the sides 15a and 15b with respect to the horizontal direction in the figure is decisive for the distance and acceleration of the end lever 13 in either shift direction.

(29) FIG. 6 shows a diagram showing curves of a travel path over time of the contacts 3a, 3b, 4a, 4b of the circuit breaker 1 with contact arrangements according to embodiments of the invention, e.g. during the opening process of the electrical switching device 1. As mentioned, exemplarily the first contact represents the nominal contact 3a of the first contact group, the second contact represents the arcing contact 4a of the first contact group, the third contact represents the nominal contact 3b of the second contact group and the fourth contact represents the arcing contact 4b of the second contact group. The axis of ordinates represents the shifting or travel distance of the contacts of the switching device 1 in millimeters and the axis of abscissae represents the time in milliseconds. The solid curve 16 shows a travel curve of the arcing contact 4b. The dashed curve 17 shows a travel curve of the nominal contact 3b and the dotted curve 18 shows the travel curve of the nominal and the arcing contact 3a, 4a. The value of zero meters represents the position in which the electrical switching device 1 is in a completely closed state and the contacts are idle or in their starting position. The positive and negative displacement values (Y-axis) of the shift values represent movements in opposite directions.

(30) As can be seen, the arcing contact 4b travels a longer distance than the nominal contact 3b. The nominal contact 3a and the arcing contact 4a travel with the same speed and acceleration and cover the same distance as they are fixedly attached together. Generally it can be seen that the contacts are accelerated at the beginning of their travel path and are decelerated towards the end of their travel path. During the opening process the mechanical coupling 2 pulls back the nominal contact 3b and the arcing contact 4b in such a way that the nominal contact 3b disconnects first from the mating nominal contact 3a and thereafter the arcing contact 4b is decoupled from the mating arcing contact 4a.

(31) During the closing process the contacts travel the curves of FIG. 6 in the opposite direction due to the nature of the mechanical coupling 2. The arcing contact 4b contacts the arcing contact 4a before the nominal contacts 3a, 3b contact one another. As can be derived from FIG. 6, the nominal contact 3b is positioned relatively close to the point where it will first touch the mating nominal contact 3a but, as it is travelling slower than the arcing contact 4b, it will reach the contact point later than the arcing contact 4b reaches its contact point with the mating arcing contact 4a. Therefore, the nominal contact 3b can be placed altogether closer to its mating contact. The advantage is that the mechanical forces acting during the movement are reduced and the required drive energy is smaller.

(32) Advantageously, the mechanical coupling is adapted such that a predefined time period between the touching or separation of the nominal contact 3a and the nominal contact 3b and the touching or separation of the arcing contact 4a and the arcing contact 4b is not exceeded.

(33) As mentioned, the mechanical coupling is advantageously adapted such that the arcing contact 4b is moved faster than the nominal contact 3b. Preferably, a speed of the nominal contact 3b and/or the arcing contact 4b is non-linear. In particular, the mechanical coupling 2 is adapted such that a speed of the third contact 3b is a first non-linear function of time and a speed of the fourth contact 4b is a second non-linear function of time, and the first and second non-linear functions are different. Additionally or alternatively the travel path of the arcing contact 4b may be longer than the travel path of the nominal contact 3b.

(34) The described contact arrangement is preferably used in an electrical switching device like an earthing device, a fast-acting earthing device, a circuit breaker, a generator circuit breaker, a switch disconnector, a combined disconnector and earthing switch, or a load break switch. Where applicable, the first contact group 3a, 4a of the electrical switching device 1 is movable along the longitudinal axis z for closing and opening said electrical switching device 1 in order to provide the actuation force transmitted to the second contact group 3b, 4b by the mechanical coupling 2 of the contact arrangement according to a predefined transmission ratio and/or speed curve. In other switching devices, in which the first contact group is fixed, the electrical switching device may comprise the additional actuator mentioned above in order to provide the actuation force transmitted to the second contact group 3b, 4b by the mechanical coupling 2 of the contact arrangement, also according to a predefined transmission ratio and/or speed curve.

(35) By providing a mechanical coupling according to the invention it is possible to make the switching device more compact even though the contacts of the switching device still have the same size. Furthermore, mechanical stress on the moving parts is reduced.

(36) For the purposes of this disclosure the fluid used in the encapsulated or non-encapsulated electric apparatus or switching device 1 can be SF.sub.6 gas or any other dielectric insulation medium, may it be gaseous and/or liquid, and in particular can be a dielectric insulation gas or arc quenching gas. Such dielectric insulation medium can for example encompass media comprising an organofluorine compound, such organofluorine compound being selected from the group consisting of: a fluoroether, an oxirane, a fluoroamine, a fluoroketone, a fluoroolefin and mixtures and/or decomposition products thereof. Herein, the terms fluoroether, oxirane, fluoroamine, fluoroketone and fluoroolefin refer to at least partially fluorinated compounds. In particular, the term fluoroether encompasses both hydrofluoroethers and perfluoroethers, the term oxirane encompasses both hydrofluorooxiranes and perfluorooxiranes, the term fluoroamine encompasses both hydrofluoroamines and perfluoroamines, the term fluoroketone encompasses both hydrofluoroketones and perfluoroketones, and the term fluoroolefin encompasses both hydrofluoroolefins and perfluoroolefins. It can thereby be preferred that the fluoroether, the oxirane, the fluoroamine and the fluoroketone are fully fluorinated, i.e. perfluorinated.

(37) In embodiments, the dielectric insulation medium is selected from the group consisting of: a (or several) hydrofluoroether(s), a (or several) perfluoroketone(s), a (or several) hydrofluoroolefin(s), and mixtures thereof.

(38) In particular, the term fluoroketone as used in the context of the present invention shall be interpreted broadly and shall encompass both fluoromonoketones and fluorodiketones or generally fluoropolyketones. Explicitly, more than a single carbonyl group flanked by carbon atoms may be present in the molecule. The term shall also encompass both saturated compounds and unsaturated compounds including double and/or triple bonds between carbon atoms. The at least partially fluorinated alkyl chain of the fluoroketones can be linear or branched and can optionally form a ring.

(39) In embodiments, the dielectric insulation medium comprises at least one compound being a fluoromonoketone and/or comprising also heteroatoms incorporated into the carbon backbone of the molecules, such as at least one of: a nitrogen atom, oxygen atom and sulphur atom, replacing one or more carbon atoms. More preferably, the fluoromonoketone, in particular perfluoroketone, can have from 3 to 15 or from 4 to 12 carbon atoms and particularly from 5 to 9 carbon atoms. Most preferably, it may comprise exactly 5 carbon atoms and/or exactly 6 carbon atoms and/or exactly 7 carbon atoms and/or exactly 8 carbon atoms.

(40) In embodiments, the dielectric insulation medium comprises at least one compound being a fluoroolefin selected from the group consisting of: hydrofluoroolefins (HFO) comprising at least three carbon atoms, hydrofluoroolefins (HFO) comprising exactly three carbon atoms, trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234ze), 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), trans-1,2,3,3,3 pentafluoroprop-1-ene (HFO-1225ye (E-isomer)), cis-1,2,3,3,3 pentafluoroprop-1-ene (HFO-1225ye (Z-isomer)), and mixtures thereof.

(41) The dielectric insulation medium can further comprise a background gas or carrier gas different from the organofluorine compound (in particular different from the fluoroether, the oxirane, the fluoroamine, the fluoroketone and the fluoroolefin) and can in embodiments be selected from the group consisting of: air, N.sub.2, O.sub.2, CO.sub.2, a noble gas, H.sub.2; NO.sub.2, NO, N.sub.2O; fluorocarbons and in particular perfluorocarbons, such as CF.sub.4; CF.sub.3I, SF.sub.6; and mixtures thereof.

(42) While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may otherwise variously be embodied and practised within the scope of the following claims. Therefore, terms like preferred or in particular or particularly or advantageously, etc. signify optional and exemplary embodiments only.

LIST OF REFERENCE NUMERALS

(43) 1=circuit breaker 2=mechanical coupling 2=first linkage 2=second linkage 2a=insulating nozzle 2b=connecting rod 3=electric arc 3a=first nominal contact 3b=second nominal contact 4a=first arcing contact 4b=second arcing contact 5=shell 5a=shielding 6a=first kinematic chain of first linkage 6b=second kinematic chain of first linkage 6c=first kinematic chain of second linkage 6d=second kinematic chain of second linkage 7, 7, 7a, 7a=first lever of kinematic chains 8a=end lever of first kinematic chain of first linkage 8b=end lever of second kinematic chain of first linkage 8c=end lever of first kinematic chain of second linkage 8d=end Sever of second kinematic chain of second linkage 9=bearing of first linkage 9a=bearing of second linkage 10a=joints between levers and contacts, end joints 10b=joints between two levers, common joints 12a=first end lever 12b=second end lever 13=guide rail end lever 14=fixed joint 15=guide rail of end lever 15a=first side of guide rail 15b=second side of guide rail 16=travel curve of fourth contact 17=travel curve of third contact 18=travel curve of first and second contact 30-36=double arrows representing moving directions s=mechanical coupling according to the prior art z=longitudinal axis