Tap changer and vacuum interrupter for a tap changer of this kind

Abstract

A tap changer for uninterrupted switching between winding taps of a tapped transformer has first and second load branches for each phase to be switched. Each load branch has a main vacuum switch and in parallel thereto a series connection of a switch-over resistance and a respective auxiliary vacuum switch. First and second vacuum switching tubes each contain the main vacuum switch of the respective first and second load branches and the auxiliary vacuum switch of the other of the load branches.

Claims

1. A tap changer for uninterrupted switching over between winding taps of a tapped transformer, the tap changer comprising: first and second load branches for each phase to be switched, each load branch including a main vacuum switch and in parallel thereto a series connection of a switch-over resistance and a respective auxiliary vacuum switch a single first vacuum switching tube holding the main vacuum switch of the first load branch and the auxiliary vacuum switch of the second load branch, a single first movable contact in the single first vacuum switching tube, two fixed first contacts in the single first vacuum switching tube and selectably connectable by the single first movable contact, a single second vacuum switching tube holding the main vacuum switch of the second load branch and the auxiliary vacuum switch of the first load branch, a single second movable contact in the single second vacuum switching tube, two fixed first contacts in the single second vacuum switching tube and selectably connectable by the single second movable contact, the first and second movable contacts of the first and second vacuum switching tubes being connected directly or through mechanical switching elements with a common load.

2. The tap changer according to claim 1, wherein each vacuum switching tube comprises: a common housing centered on and rotation-symmetrical to an upright longitudinal axis, a single axially movable plunger in the housing, a lower fixed contact terminal in the housing below the single axially movable plunger, a single movable contact member on the movable plunger, a lower fixed contact member on the lower contact terminal, and an upper fixed contact member in the housing above the lower fixed contact member and positioned such that, on downward movement of the movable plunger, the single movable contact member disengages from the upper fixed contact member and then engages the lower fixed contact member.

3. The tap changer according to claim 2, wherein the upper fixed contact member extends perpendicular to the longitudinal axis in a plane.

4. The tap changer according to claim 2, wherein the upper fixed contact member at least partly surrounds the plunger.

5. The tap changer according to claim 2, wherein the fixed upper contact member is connected directly to the respective tap and the lower fixed contact member is connected via a respective switchover resistance to the respective tap.

6. The tap changer according to claim 2, wherein the single movable contact member selectively contacts each of the first fixed upper contact member and the fixed lower contact member directly.

7. The tap changer according to claim 2, wherein the single movable contact member has first and second opposing surfaces, and in a first position of the single movable contact member, the first surface directly contacts the upper fixed contact member, and in a second position of the single movable contact member, the second surface directly contacts the lower fixed contact member.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention shall be explained in more detail in the following by way of example with reference to drawings, in which:

(2) FIG. 1 shows a tap changer according to the prior art,

(3) FIG. 2 shows a changeover sequence of such a known tap changer,

(4) FIG. 3 shows a vacuum switching tube according to the invention,

(5) FIG. 4 shows a tap changer according to the invention with two vacuum switching tubes according to the invention in schematic illustration and

(6) FIG. 5 shows a further tap changer according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(7) A known tap changer is shown in FIG. 1. It has a first load branch in which a vacuum switching tube MSV.sub.a acting as a main switch as well as parallel thereto a switch-over resistance R.sub.a and a vacuum switching tube TTV.sub.a acting as a resistance switch. In entirely analogous manner, the second load branch comprises a vacuum switching tube MSV.sub.b as well as parallel thereto a further switch-over resistance R.sub.b and a vacuum switching tube TTV.sub.b. The known tap changer thus has two vacuum switching cells per load branch, therefore four vacuum switching cells per phase in total.

(8) FIG. 2 shows the switching sequence of such a known tap changer in the case of changeover from the winding tap n to the winding tap n+1. The starting position, in which the tap n is electrically connected, corresponds with the setting of the individual switching elements illustrated in FIG. 1. The changeover takes place in the following steps: MSV.sub.a opens TTV.sub.b closes TTV.sub.a opens MSV.sub.b closes;
the changeover is concluded.

(9) FIG. 3 shows a combined vacuum switching tube according to the invention. It has a common housing 1. Provided centrally on the longitudinal rotation-symmetry axis s1 is an upper movable plunger 2 and, at the opposite end, a lower fixed contact terminal 3. The movable plunger 2 carries a movable contact member 4 at its inner free end. The fixed lower contact terminal 3 itself carries a fixed contact member 5. Provided above the movable contact member 4 is an upper encircling annular stationary contact arrangement 6 that extends perpendicular to the longitudinal rotation-symmetry axis S1 in the plane S2 that is here illustrated to be horizontal. A fixed contact 8, which is, for example, soldered, is fastened to the contact arrangement 6. The fixed contact 8 is, in an end setting of the movable plunger 2, electrically contactable by the contact member 4 thereof. In the other end setting this contact member 4 electrically connects the stationary contact member 5 of the lower contact terminal 3. The movable contact member 4 can thus electrically connect, in the manner of a changeover switch, selectably not only the stationary contact 8, but also the stationary contact member 5. Bellows 7 are illustrated as well as upper and lower ceramic members 9, 10, and in the interior of the housing 1 an upper attenuating screen 11 and a lower attenuating screen 12.

(10) Overall, several advantages are achieved with the tap changer according to the invention with vacuum switching tubes according to the invention: The number of vacuum switching tubes necessary is de facto halved; the need for space for these switching elements is correspondingly smaller. Costs are similarly reduced. This is achieved by the vacuum switching tube used in accordance with the invention that is constructed as a tandem tube and, in particular, contains two separate switches, but only a single movable contact.

(11) In that case, the vacuum switching tube according to the invention is of simple construction; by contrast to the solutions known from the prior art it needs neither internally disposed contact compression springs nor complicated actuating mechanisms or special cage-like contact constructions.

(12) FIG. 4 shows schematically a tap changer with two load branches, as has already been explained in FIGS. 1 and 2. It can be seen that here, according to the invention, the vacuum switching tube MSV.sub.a acting as a main switch of the first load branch and the vacuum switching tube TTV.sub.b acting as a resistance switch of the second load branch are combined into a first vacuum switching tube V1 according to the invention. Equally, the vacuum switching tube MSV.sub.b acting as a main switch of the second load branch and the vacuum switching tube TTV.sub.b acting as a resistance switch of the first load branch are combined into a second vacuum switching tube V2 according to the invention.

(13) This takes place in that in the case of the first vacuum switching tube V1 according to the invention, for example, the contact path between fixed contact member 5 and movable contact member 4 connected to the load L takes over the function of the main switch MSV.sub.a, and the contact path between fixed contact 8 and movable contact member 4 takes over the function of the resistance switch TTV.sub.b. In entirely analogous manner in the case of the second vacuum switching tube V2 according to the invention, for example, the contact path between the fixed contact member 5 and movable contact member 4 takes over the function of the main switch MSV.sub.b, the contact path between fixed contact 8 and movable contact member 4 takes over the function of the resistance switch TTV.sub.a. Obviously, other electrical connections of the contact paths of the two vacuum switching tubes V1, V2 are also possible within the scope of the invention.

(14) FIG. 5 shows a further tap changer according to the invention, in which additional mechanical switching elements (MDC.sub.a, MDC.sub.b) are provided that serve for electrical insulation of the load branch not conducting the load current to the load LA.

(15) In all forms of embodiment the advantage of the invention consists in that only two vacuum switching tubes each with only one movable contact member, which is to be driven, are required in order to replace in total four separate vacuum switching tubes in the two load branches.