The invention relates to the field of medium and high voltage switching technologies and concerns an electrical switching device according to the independent claim, particularly for a use as an earthing device, a fast-acting earthing device, a circuit breaker or a disconnector switch in power distribution systems.
Electrical switching devices are well known in the field of 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 document the term high voltage refers to voltages higher than 72.5 kV and the term medium voltage refers to voltages between 1 kV and 72.5 kV. The electrical switching devices, like the 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 contact fingers for the nominal current. When disconnecting a nominal current within the electrical switching devices, the current commutates from the nominal contacts of the electrical switching device to its arcing contacts.
It is an objective of the present invention to enhance an electrical switching device in terms of robustness by preventing damage to its contact fingers.
This objective is solved by an electrical switching device for medium or high voltage circuits having at least a nominal contact arrangement is provided. Its nominal contact arrangement comprises at least a first nominal contact comprising a plurality of contact fingers forming a finger cage. The finger cage is concentric with respect to a longitudinal axis. The contact fingers are separated from one another by empty slots extending up to a free end of the contact fingers. The nominal contact arrangement further comprises at least a mating second nominal contact. At least one of the nominal contacts is movable parallel to the longitudinal axis and cooperates with the other nominal contact for closing and opening the electric switching device.
In an ideal case all contact fingers of a known electrical switching device, e.g. a circuit breaker, would be separated from the mating nominal contact simultaneously. In practical embodiments of known circuit breakers or switches some of the contact fingers separate later than the rest of the contact fingers. Thus, before commuting to the arcing contact, the current still flows through the contact fingers that are still in contact with the mating nominal contact, for a period of time. It is only when these contact fingers have also lost contact with the mating nominal contact that the current switches to the arcing contacts. During the period when the entire current flows through the contact fingers which have separated later, significant electromagnetic forces act on these contact fingers and can deform them permanently. The deformation manifests itself in that adjacent fingers are attracted towards one another as a result of the Lorentz-force and may therefore be bent in a non-radial direction with respect to the longitudinal axis.
Thus, in order to minimize the risk of damage, according to the invention the empty slots comprise first and second empty slots. The second empty slots are shorter than the first empty slots. Furthermore, the contact fingers are grouped in groups, with the fingers of each group being separated by second empty slots and the fingers of adjacent groups being separated by first empty slots.
By grouping the contact fingers, the overall circumferential stiffness is increased, with the result that the bending of the contact fingers is avoided or at least reduced or minimized. It is noted here that the empty slots are necessary in order to decrease the radial stiffness of the first nominal contact and provide a certain elasticity such that the second nominal contact can mechanically contact the first nominal contact by force fit, that is, the second tube-shaped nominal contact is inserted into the finger cage by displacing the contact fingers radially outwards with respect to the longitudinal axis when the electrical switching device is closed. The required elasticity of the contact fingers is also advantageous in order to compensate for manufacturing tolerances of the nominal contacts.
In an embodiment each group of contact fingers comprises at least two contact fingers. In another embodiment each group of contact fingers comprises at least three contact fingers.
The higher the number of contact fingers is, the higher electromagnetic forces the contact fingers can withstand. Thus, the electrical switching device can be designed in a flexible way by choosing a number of contact fingers per group such that they can withstand the specific currents flowing through them in that particular electrical switching device.
In yet another embodiment the groups each have the same number of contact fingers. This advantageously ensures that the stiffness of the finger cage is evenly distributed for all contact fingers.
Further embodiments, advantages and applications of the invention result from the dependent claims and from the following description of the figures.
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 in the “Background”-section, such as in an earthing switch, fast-acting earthing switch, disconnector, combined disconnector and earthing switch, load break switch, generator circuit breaker, and generally in any switch. The most preferred use is in switches for high voltage and medium voltage.
A “closed configuration” as used herein means that nominal contacts of the circuit breaker are closed and are thus conducting a nominal current.
The circuit breaker 1 comprises a chamber enclosed by a shell or enclosure 5 which normally is cylindrical around the longitudinal axis z. It further comprises a nominal contact arrangement formed by a first nominal contact comprising a plurality of contact fingers 3a, of which only one is shown here for reasons of clarity. The nominal contact arrangement is formed as a finger cage around the longitudinal axis z. The term “finger cage” as used herein refers to an arrangement, for example a cylindrical or conical or oval arrangement, of the contact fingers around the longitudinal axis z. A shielding 9 can be arranged around the finger cage. The nominal contact arrangement further comprises a second mating contact 3b which normally is a metal tube. The contact fingers 3a and the second contact 3b are movable relatively to one other from the closed configuration shown in
The contact fingers 3a are attached to or can be a part of a finger support 2, particularly a metal support cylinder 2.
The circuit breaker 1 furthermore comprises an arcing contact arrangement formed by a first arcing contact 4a and a second arcing contact 4b.
The first nominal contact and the first arcing contact 4a are typically not movable relatively to one another. In the same way, the second nominal contact 3b and the second arcing contact 4b are not movable with respect to one another. For the explanatory purposes of the present invention it is assumed that only the second nominal contact 3b and the arcing contact 4b are movable and the finger cage is stationary along the z-axis.
When the closed circuit of
In embodiments, each contact finger 6, 7 is adjacent to at least one second empty slot 8. Thus, there are no contact fingers which are adjacent to only first slots 10, which would again decrease their stiffness.
In embodiments, the total number of the contact fingers 6, 7 is not a prime number. By this, it is ensured that all contact fingers 6, 7 can be grouped in suitable groups which all comprise the same number of fingers without occurrence of ungrouped contact fingers 6, 7. Of course, for this purpose the total number of contact fingers 6, 7 has to be a multiple of the number of contact fingers 6, 7 in one group 5.
In one embodiment of the invention all the second empty slots 8 have the same length (
In embodiments, the second empty slots 8 are shorter than the first empty slots 10 by at least 50%. This ensures that both criteria, a good radial flexibility and a good circumferential stiffness, are met.
The contact fingers 6, 7 are elastically deformed in a radial direction upon closing the electrical switching device, here the circuit breaker 1.
As mentioned, the contact fingers 6, 7 form the finger cage. Particularly, the contact fingers 6, 7 are formed by a tubular metal section 12. The first and second empty slots 10, 8 extend from a first end into the tubular metal section and the contact fingers 6, 7 are interconnected at a second end of the tubular metal section, as shown in
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” signify optional and exemplary embodiments only.
Number | Date | Country | Kind |
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12192466 | Nov 2012 | EP | regional |
Number | Name | Date | Kind |
---|---|---|---|
1978246 | Bauerschmidt | Oct 1934 | A |
3427419 | Findley, Jr. | Feb 1969 | A |
4012608 | Lockard | Mar 1977 | A |
4319105 | Lott | Mar 1982 | A |
4553008 | Veverka et al. | Nov 1985 | A |
5820413 | Yamada | Oct 1998 | A |
5981893 | Bleiker et al. | Nov 1999 | A |
20040216988 | Receveur et al. | Nov 2004 | A1 |
Number | Date | Country |
---|---|---|
4212740 | Oct 1993 | DE |
102004061276 | Jun 2006 | DE |
0844631 | May 1998 | EP |
Entry |
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European Search Report Application No. EP 12 19 2466 Completed: Apr. 18, 2013; Mailing Date: Apr. 25, 2013 4 pages. |
Number | Date | Country | |
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20140131183 A1 | May 2014 | US |