This application is the US-national stage of PCT application PCT/EP2011/000859 filed 23 Feb. 2011, published 17 Nov. 2011 as WO2011/141081, and claiming the priority of German patent application 102010019948.6 itself filed 8 May 2010.
The invention relates to an on-load tap changer for uninterrupted switching over between winding taps of a tapped transformer having a selector for power-free preselection of the winding tap that is to be switched to and a load changeover switch for the actual load changeover from the previous winding tap to the preselected winding tap.
Such a known load changeover switch typically has two main current branches and two auxiliary current branches. The first main current branch electrically connects the first winding tap to a load shunt via a vacuum switching tube, the second main load branch electrically connects the second winding tap to the load shunt via a further vacuum switching tube, the first auxiliary current branch connects the first winding tap to the load shunt via a series connection of a further vacuum switching tube and at least one switch-over resistance, and the second auxiliary current branch connects the second winding tap to the load shunt via a series connection of a further vacuum switching tube and at least one further switch-over resistance.
Such a load changeover switch having in total four vacuum switching tubes per phase is known from DE 2021575 A. A respective vacuum switching tube as main contact and a respective further vacuum switching tube that is in series connection with a switch-over resistance, as resistance contact are provided in each of the two load branches respectively connected with a winding tap. In a case of uninterrupted load changeover from the previous winding tap n to the new, preselected winding tap n+1 initially the main contact of the side being switched off is opened and thereupon the resistance contact of the side taking over closes so that a compensating current limited by the switchover resistors flows between the two winding taps n and n+1. After the previously closed resistance contact of the side switching off has opened, the main contact of the side taking over then closes so that the entire load current leads from the new winding tap n+1 to the load shunt; the changeover is thus concluded.
However, in different cases of use of such known on-load tap changers with vacuum switching tubes for regulation of power transformers a high surge-voltage strength of up to 100 kV and significantly above that is required. Such undesired surge voltages, the level of which is substantially dependent on the construction of the tapped transformer and the winding parts between the individual tap steps, are on the one hand lightning surge voltages that result from lightning strikes in the mains. On the other hand, switching surge voltages can also occur that are caused by unpredictable switching surges in the mains to be regulated. In the case of insufficient surge-voltage strength of the on-load tap changer a transient step short-circuit or undesired disruption of the ceramic or the damping screen of vacuum switching tubes in the load branch not conducting the load current can occur, which not only can cause long-term damage thereof, but is generally undesirable.
In order to combat excessive surge-voltage loads it is already known from DE 2357209 [U.S. Pat. No. 3,934,174] and DE 2604344 to provide protective spark gaps or voltage-dependent resistors or both between the load branches; however, these means are, in various cases, insufficient and are unable to exclude or completely exclude harmful surge voltage loads in their effect.
The object of the invention is to indicate an on-load tap changer of the kind stated in the introduction with high surge-voltage strength and at the same time high switching power.
This object is fulfilled by an on-load tap changer in which a further, separately actuatable mechanical contact is provided in each of the two main current branches and in each of the two auxiliary current branches between the respective winding tap and the respective vacuum switching tube such that the vacuum switching tubes in the main current branch and the vacuum switching tubes in the auxiliary current branch of the unconnected winding tap are electrically separable from this tap.
The invention is based on the general idea of achieving an electrical separation, i.e. separation of potential, of the vacuum switching tubes in the respective branch that is not conducting load current from the respective winding tap by additional mechanical switching elements that are respectively arranged between the vacuum switching tubes and the respective winding tap with which they are electrically connected. Possibly occurring surge voltages are thereby harmless to the vacuum switching tubes in each load branch not conducting the load current. This applies equally to vacuum switching tubes operating as a main contact as well as those operating as a resistance contact.
The invention shall be explained in more detail in the following by way of example with reference to drawings in which:
The load changeover switch of an on-load tap changer according to the invention is illustrated in detail in
The on-load changeover switch has, as also known from the prior art, two load branches A and B that are respectively electrically connected with a winding tap n or n+1. The on-load tap changer according to the invention has a main current branch and a resistance current branch in each load branch.
The first main current branch produces an electrical connection from the winding tap n to the load shunt LA through a vacuum switching tube MSVa. The second main current branch produces an electrical connection from the winding tap n+1 to the load shunt LA through a vacuum switching tube MSVb. The first auxiliary current branch that is provided in parallel with the first main current branch produces an electrical connection from the winding tap n to the load shunt through a further switching tube TTVa and at least one first switch-over resistance Ra arranged in series therewith. The second auxiliary current branch that is provided in parallel with the second main current branch produces an electrical connection from the winding tap n+1 to the load shunt through a further switching tube TTVb and at least one second switch-over resistance Rb arranged in series therewith.
According to the invention, a further, separately actuatable mechanical contact is provided in each of the main current branches and in each of the auxiliary branches between the respective winding tap n or n+1 and the respective vacuum switching tube MSVa, TTVa—or on the other side, MSVb, TTVb—electrically connected therewith. Thus, in total four such mechanical contacts are present:
In
According to a preferred form of embodiment of the invention, additionally provided in each load branch, as also illustrated in
In
The on-load tap changer according to the invention thus makes it possible to completely electrically separate the vacuum switching tubes in the respective branch that is not conducting load current from the respective winding tap and thus to provide protection from surge-voltage loads.
A complete switching sequence of the on-load tap changer according to the invention in the case of switching-over of the basic setting shown in
It can be seen that in the case of the explained switching sequence it is ensured that in each instance the vacuum switching tubes of the side not conducting load current are completely electrically separated from the unconnected winding tap by the corresponding mechanical contacts; the object of the invention is fulfilled.
Number | Date | Country | Kind |
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10 2010 019 948 | May 2010 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2011/000859 | 2/23/2011 | WO | 00 | 11/9/2012 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2011/141081 | 11/17/2011 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3039041 | Jansen | Jun 1962 | A |
3934174 | Bleibtreu | Jan 1976 | A |
3935407 | Bleibtreu et al. | Jan 1976 | A |
Number | Date | Country |
---|---|---|
2021575 | Dec 1971 | DE |
2604344 | Aug 1977 | DE |
02216805 | Aug 1990 | JP |
WO 0231846 | Apr 2002 | WO |
Number | Date | Country | |
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20130057248 A1 | Mar 2013 | US |