Patent Application
20140175061
The invention relates to the field of medium and high voltage switching technologies and concerns a contact arrangement and an electrical switching device with such a contact arrangement according to the independent claims, particularly for a use 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 in power transmission and distribution systems.
Electrical switching devices are well known in the field of medium and high voltage switching applications. They are e.g. used for interrupting a current when an electrical fault occurs. As an example for an electrical switching device, circuit breakers have the task of opening contacts and keeping them far apart from one another in order to avoid a current flow, even in case of high electrical potential originating from the electrical fault itself. For the purposes of this disclosure the term medium voltage refers to voltages from 1 kV to 72.5 kV and the term high voltage refers to voltages higher than 72.5 kV. The electrical switching devices, like said circuit breakers, may have to be able to carry high nominal currents of 5000 A to 6300 A and to switch very high short circuit currents of 63 kA to 80 kA at very high voltages of 550 kV to 1200 kV.
Because of the high nominal current, the electrical switching devices of today require many so-called nominal contact fingers for the nominal current. When disconnecting (opening) a nominal or short circuit current within the electrical switching devices, the current commutates from nominal contacts of the electrical switching device to its arcing contacts. When connecting (closing) the nominal contacts of the electric switching device, also the arcing contacts are connected. They normally comprise as a first arcing contact arcing contact fingers arranged around the longitudinal axis of the electrical switching device in a so-called arcing finger cage and, as a second arcing contact, a rod which is driven into the finger cage.
During the closing and opening process of the electrical switching device an electric arc forms between the first and the second arcing contact, which damages the contacts over time. In order to minimize this damage the electrical switching devices contain a fluid used to quench the electric arc as fast as possible. Another measure is to limit the time period for the entire closing and opening process of the nominal and arcing contacts, particularly the time period or time interval between contacting the nominal contacts and contacting the arcing contacts or between separating the nominal contacts and separating the arcing contacts. This time constraint results in the necessity of accelerating and decelerating the nominal contact and the arcing contact on one side of the electrical switching device according to the given time period. The contacts have to have a certain cross-section in order to be able to carry the required current. Very high voltage circuit breakers require a longer distance between contacts in an opened state in order to avoid electrical breakdown. Hence, considerable forces are necessary to accelerate and/or decelerate the contacts and the additional moving parts of the switching device. These forces may lead to increased mechanical stress on the moving parts of the contact arrangement and even to mechanical failures, thus reducing the lifetime of such an electrical switching device. Furthermore, particles are generated during the switching process of the circuit breaker, which can result in dielectric failures.
Thus, it is an objective of the present invention to improve a contact arrangement with respect to the above mentioned disadvantages. This task is solved by the contact arrangement and circuit breaker of the independent claims. Embodiments are given by dependent claims and their combinations.
In a first aspect of the invention the objective is solved by a contact arrangement having a longitudinal axis and comprising a first contact group with a first and a second contact and a second contact group with a third and a fourth contact. The first contact interacts electrically and mechanically with the third contact for closing and opening the contact arrangement. Additionally or alternatively 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.
By designing the mechanical coupling in said way it is possible to decrease the forces acting on the contacts. This is due to the fact that the accelerations and/or decelerations of the third or the fourth contact, respectively, can be chosen to be different from one another, having values which take into account their respective travel path. For example, if the travel path of the fourth contact is longer than the travel path of the third contact, the acceleration of the third contact can be reduced. Consequently, mechanical stress on the moving parts of the contact arrangement or the switching device is reduced. Furthermore it is possible to fine-tune the time periods between the closing of the first and third contact and the closing of the second and fourth contact independently from one another, and/or between the opening of the first and third contact and the opening of the second and fourth contact independently from one another.
In a second aspect of the invention the objective is solved by an electrical switching device comprising such a contact arrangement. For closing and opening said electrical switching device the first contact group is movable along the longitudinal axis 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. Said actuation force can alternatively be provided by an actuator of the electrical switching device.
The first alternative is advantageously used in circuit breakers for which both contact groups are movable relatively to one another for closing and/or opening the electrical switching device. By using the first contact group for actuating the second contact group it is possible to save up additional actuators and thus to reduce the cost of the switching device.
The second alternative is advantageously used in circuit breakers for which only the second contact group is movable and the first contact group is fixed. In this case said actuator is used for moving the second contact group.
In embodiments, the first and the third contact are nominal contacts, and/or the second and the fourth contact are arcing contacts.
Advantageously, the at least one mechanical coupling is a linkage having a first and a second kinematic chain. The first kinematic chain is movably connected to the first contact group, particularly by an intermediary member, in an electrically insulating manner. The second kinematic chain is movably connected to the second contact group.
By using at least a linkage as a mechanical coupling, the transmission of an actuating force to the second contact group is simplified, thus reducing cost.
In one embodiment the mechanical coupling comprises a first and a second linkage. The end links of the first kinematic chain of each one of the linkages are pivotably connected to the first contact group in such a way that they are commonly moved by the first contact group, in particular are moved simultaneously. Advantageously, an end link of the second kinematic chain of each one of the linkages is pivotably connected to the third contact or the fourth contact, respectively. By this it is possible to keep the linkages simple. Advantageously, 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.
By using two linkages with different transmission ratios a higher flexibility is achieved with regard to the travel path of the third and the fourth contact.
In another embodiment the mechanical coupling comprises only one linkage and the second kinematic chain of the linkage comprises two end links, one of which is connected at one end to the third contact and the other one is connected at one end to the fourth contact. This is a cost-saving and space-saving design. In one embodiment each end link of the second kinematic chain is pivotably connected to a neighbouring link of the second kinematic chain by a distinct joint. In an alternative embodiment the two end links of the second kinematic chain are connected to a neighbouring link of the second kinematic chain by a common joint. Advantageously, the common joint connects one of the end links of the second kinematic chain pivotably with the fourth contact and the other end link of the second kinematic chain is connected fixedly to the third contact, and in particular comprises a guide rail guiding the common joint. Advantageously, a transmission ratio between the first kinematic chain and the second kinematic chain with one of its end links is not equal to a transmission ratio between the first kinematic chain and the second kinematic chain with the other one of its end links.
Embodiments, advantages and applications of the invention result from the dependent claims and from the now following description by means of the figures. It is shown in:
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.
In the following same reference numerals denote structurally or functionally same or similar elements of the various embodiments of the invention.
The circuit breaker 1 is enclosed by a shell 5 which normally is 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.
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, into an opened configuration shown in
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.
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.
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
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
As mentioned above, a 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 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 joint 10a.
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 links, are constrained by their connections to other links. The links for the mechanical coupling s may e.g. be metal bars.
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.
The end links 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).
It shall be noted that the usage of an alternative actuator for the first linkage 2′ and the second linkage 2″ is possible for all embodiments of the mechanical coupling 2 (e.g. of
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
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 links 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 links 8a and 8c with the respective first links 7, 7a are pushed in the direction of the arrows 32. The respective first links 7, 7a thereby rotate about their corresponding bearing 9, 9a (arrows 33), causing the joints 10b between the first links 7′, 7a′ and the end links 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 links 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 link 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 links 8b, 8d determine the shifting distance of the respective contact 3b, 4b and/or their shifting speed.
As can be seen in
The movement of the moving parts is in this embodiment analogous to the movement of one of the linkages 2′, 2″ of
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 closing 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.
During the closing process the contacts travel the curves of
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.
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.
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.
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.
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.
