CA2311781A1

CA2311781A1 - Selector switch

Info

Publication number: CA2311781A1
Application number: CA002311781A
Authority: CA
Inventors: Wolfgang Albrecht; Dieter Dohnal
Original assignee: Individual
Current assignee: Maschinenfabrik Reinhausen GmbH
Priority date: 1998-05-14
Filing date: 1999-03-25
Publication date: 1999-11-25
Also published as: RU2221301C2; BR9907918A; BR9907918B1; HUP0100062A2; HK1033613A1; DE59901305D1; CZ20004212A3; CN1275241A; WO1999060588A1; CZ298858B6; EP1078380B1; PL344005A1; AU3417899A; HUP0100062A3; DE19821775C1; ATE216801T1; KR100420630B1; EP1078380A1; HU223171B1; BG104589A

Abstract

The invention relates to a selector switch for tapped transformers to enable continuous tap switching with respect to a tapped winding, whereby fixed stepped contacts are arranged inside a cylinder made of insulating material on a horizontal plane for each phase. A rotating actuating shaft is located inside the insulating cylinder. The actuating shaft has a moveable hinged contact carrier for each phase that is to be switched and vacuum switching cells are respectively and vertically arranged on said contact carrier.

Description

21457 PCT/EP99/02020 Transl. of WO 99/60588 The invention relates to a load selector for tapped transformers according to the introductory clause of the first claim. Such load selectors are known from German 3,833,126.
Load selectors are used on transformers to switch the taps of the control windings of these transformers under load and thus to compensate accurately for voltage variations. Load selec-tors are less expensive to make and use since they do not separate the functions of selector and load switch. During the switching process the various contacts draw arcs.
In order to avoid this, German 3,833,126 proposes a load selector wherein each phase being switched is provided with two jointly moved mechanical switch contacts on a common contact support and a respective vacuum switch is provided on the contact support in series with each of the movable mechanical switch contacts. The stationary tap contacts engaged by the swingable mechanical switch contacts of the load switch are arranged on a concentric circle on the surface of an insulating cylinder. The vacuum switches are mounted horizontally on the contact support and are operated by a cam lying on a further concentric circle that is provided axially between the ring of fixed tap contacts and an additional commutating ring.
Both of these load selectors have several disadvantages.
First, as a result of the horizontal orientation of the vacuum 21457 PCT/EP99/02020 Transl, of WO 99/60588 switches on the common contact support the insulating cylinder and thus the load switch must be of excessively large diameter. Vacuum switches have certain minimum dimensions depending on their ratings and in particular are fairly long: Furthermore the actuating stem of the vacuum switch projects longitudinally from it. It is therefore clear that the common contact support has a radial dimension determined by the dimensions of the vacuum switch and its actuating means, and this in turn determines the diameter of the load selector.
In addition to these general problems of size there is the considerable disadvantage with horizontal installation of the vacuum switches according to the state of the art that when the load selector is filled with oil, air is trapped in the top of the folds of the vacuum-switch cuff and the oil cannot fill this region. This results when the vacuum switch is actuated in an uneven loading of the vacuum-switch cuff, creating the danger that it ruptures. Such trapping of air in the vacuum-switch cuff can only be avoided with horizontal vacuum switches by filling the load selector in a vacuum; such vacuum filling is however not possible or is excessively expensive at the site, that is during service or repair.
It is furthermore important that load selectors normally also have a considerable length, that is height. The fixed tap contacts of the individual phases to be switched are arranged in circles one above the other, the means for actuating the rotatable switching shaft are provided inside the load selector which carries 21457 PCT/EP99/02020 Transl. of WO 99/60588 the contact support of each phase, and at the top and bottom of the load selector are means for holding its switching shaft, so that in general, as stated, the load selector is fairly long. The result is that the switching shaft inside it is also fairly long.
Such switching shafts are normally made of GFK or another insulating material and metal switching shafts have also been suggested. The contact supports are secured with the known load selectors by means of screws to the switching shaft. German 4,414,941 describes fixing the contact support on the switching shaft by means of a clamping flange.
Tolerance errors, different coefficients of expansion of the oil-filled housing and the switching column, and bending can create problems in the known load selectors with the interaction of the elements carried on the individual contact supports, in partic-ular the vacuum switches which work with the annular actuating means, because the actuating stems of the vacuum switches normally move through a relatively short linear stroke.
It is an object of this invention to avoid these disad-vantages and to provide a load selector of the known type that efficiently positions the vacuum switches and ensures their accu-rate and sure actuation under all operating conditions.
This object is attained by the load selector of the first patent claim. The dependent claims relate to particularly advanta-geous features of the invention.

21457 PCT/EP99/02020 Travel. of WO 99/60588 With the load selector according to the invention the vacuum switches are mounted upright on the contact support. The contact supports have slide contacts that are exactly guided by rollers in an output ring. Bumps in this output ring control the vacuum switches. Slide contact blades that are provided in the contact support conduct the current to the output ring. Further slide contact blades on the contact support assist conducting the current.
According to a further feature of the invention the contact supports are each movable on the switching shaft. The particular advantage of the load selector according to the inven-tion is, in addition to its small size, that the overall forces for actuating the vacuum switches as well as the contact force are axially transmitted via the output ring and the fixed contacts to the stable oil-holding housing. In this manner radial stressing of the switching column, in particular enough to make it bend, and the change in switching times of the vacuum switches this causes are avoided with a reduction of the contact forces. With the rotatable and axially displaceably mounted contact supports that are guided axially by the output ring, the switching sequence is ensured even with considerable axial shift caused by differential thermal expansion of the switching column and the oil-filled housing.
The invention is more closely described in the following by way of the exemplary drawing. Therein:

21457 PCT/EP99/02020 Transl, of WO 99/60588 FIG. 1 is a first embodiment of a load selector according to the invention seen in section from the side;
FIG. 2 is a portion of the contact support of this load selector in section seen from above;
FIG. 3 is a second embodiment of the load selector according to the invention seen in section from the side;
FIG. 4 is a schematic diagram of the circuit of the load selector according to the invention;
FIG. 5 is a modified circuit;
FIG. 6 is a typical switching sequence of a load selector according to the invention.
The load selector shown in FIG. 1 is an embodiment of the invention with a contact support 3 rotatably mounted on a switching shaft 2 and vacuum switches 27 and 28 mounted upright on it. In particular with regard to structure:
The load selector is comprised of an insulating cylinder 1 provided centrally with a longitudinally extending switching shaft 2 also of insulating material. As is known, the switching shaft 2 is rotatable, to whihc end there is normally a maltese drive which is not shown. Also not shown is the bearing in the bottom of the insulating cylinder 1 for the switching shaft 2.
The switching shaft 2 carries at each plane of the fixed contacts 16 to be engaged and which are described more closely below a contact support 3 that is mounted on a pivot block 4 on the 21457 PCT/EP99/02020 Transl. of WO 99/60588 switching shaft 2. The pivot block 4 is fixed by screws 4.1 and 4.2 to the switching shaft 2.
The contact support 3 is formed of a bearing part 5, a support housing 6, and a contact housing 7. The individual parts of the contact support 3 are connected together by screws 8 and 9.
The contact housing 7 itself is formed in the illustrated embodi-ment of an upper contact-housing part 10 and a lower contact-housing part 11; both parts are connected together via further screws 12. The contact housing 7 can also be made in one piece.
The bearing part 5 has a bore 13 holding a bolt 14 that forms the connection with the bearing block 4 and thus permits pivoting movement. The bolt 14 is secured in place by a cross pin 15. The entire contact support 3 is thus pivotal as a unit about the bolt 14 relative to the axially nonmovable switching shaft 2.
The inside surface of the insulating cylinder 1 has, in a respective plane for each of the phases to be switched, an array of fixed tap contacts 16 electrically connected to the respective taps of the control winding of the tapped transformer to be switched.
The fixed tap contacts 16 are engageable by respective contacts 17 and 18. These contacts 17 and 18 are provided horizontally offset from each other on the contact support such that rotation of the switching shaft 2 and thus of the contact support 3 makes at least one of the contacts 17 or 18 touch the adjacent new fixed tap contact 16 before the other of these contacts has left the old fixed tap contact. The contact 17 thus works as switching contact, the other contact 18 as auxiliary contact.

21457 PCT/EP99/02020 Transl. of WO 99/60588 FIG. 2 shows in top view the two contacts 17 and 18 next to each other on the contact support 3 and the fixed tap contact 16. In the embodiment of FIG. 2 the contact 17 acting as switch contact is formed in order to carry the most possible current of two connected parts 17.a and 17.b. Each of the contacts 17 and 18 is formed of a respective upper contact part 17.1 or 18.1 as well as a lower contact part 17.2 and 18.2. In the particular embodi-ment of FIG. 2 of the switching contacts, the contact 17 thus is formed altogether of four parts, namely two upper contact parts l7.la and l7.lb as well as two lower contact parts 17.2a and 17.2b.
This double construction of the contact 17 acting as switching contact is advisable for various embodiments but not essential to the invention. The upper contact parts 17.1 and 18.1 and the lower contact parts 17.2 and 18.2 of the contacts 17 and 18 are pivotal about a separate pivot axes 19, 20, 21, and 22 on the contact housing 7. The are urged toward each other by springs 23, 24, 25, and 26 toward the fixed tap contact 16 engaged between them.
In other words: the upper contacts 17.1 and 18.1 as well as the other contact parts 17.2 and 18.2 press with a defined contact force on both sides of the respective fixed tap contact 16.
As a result of the described pivoting about the separate axes 19, 20, 21, and 22, sliding on the fixed tap contact 16 is possible.
In FIGS. 1 and 2 only the front or upper contact, pivots, and springs can be seen.
Furthermore each contact support 3 carries two vacuum switches 27 and 28 held by respective upper and lower mounting _ 7 _ 21457 PCT/EP99/02020 Transl. of WO 99/60588 collars 29, 30, 31, and 32 so that the cuffs 33 and 34 as well as the actuating stems 35 and 36 of the vacuum switches 27 and 28 extend upward. Of these described parts only the front one is shown in FIG. 1. In order to operate the actuating stems 35 and 36 of the vacuum switches 27 and 28, there are two levers 37 and 38 that each have a free end carrying a respective roller bolt 41 and 42 with a respective control roller 39 and 40. On their other ends they are effective on the respective already described actuating stems 35 and 36. Both levers 37 and 38 are pivotal on respective pivots 43, 44; it is also possible to provide a common pivot. The control rollers 39 and 40 of the levers 37 and 38 themselves ride on a control ring 45 which has an upper control surface 46 as well as a lower control surface 47. The control ring 45 extends radi-ally inward from the inner surface of the insulating cylinder 1.
FIG. 1 shows how the first control roller 39 rolls on the lower control surface 47 and the second control roller 40 on the upper control surface 46. The two control surfaces 46 and 47 thus serve to actuate the vacuum switches 27 and 28 in that as the respective control rollers 39 and 40 ride onto a bump the respective levers 37 and 38 will pivot about their pivots 43 and 44 and thus operate the actuating stem 35 or 36 of the respective vacuum switch 27 or 28.
In addition on the inside of the insulating cylinder 1 is an output contact ring 48 that has an outwardly leading contact element 49 and serves for connection to the load. In particular the control ring 45 and the output contact ring 48 can be formed as a single part of a conducting material as shown in FIG. 1. The _ g _ 21457 PCT/EP99/02020 Transl. of WO 99/60588 output contact ring 48 on its side is associated with a mechanical output contact 50 that is provided on the contact support 3 and that like the already described contacts 17 and 18 is formed of an upper output contact part 50.1 and a lower contact part 50.2. Both of these output contact parts 50.1 and 50.2 are similarly mounted on respective pivots 53 and 54 and are pressed together by respec-tive springs 51 and 52 so that they grip the output contact ring 48 with a defined contact pressure.
Finally the contact support 3 has two further rollers 55 and 56 that roll on opposite faces of the output contact ring 48 ant thus guide the entire contact support 3. With this described system tolerance problems of all kinds are compensated for, in particular bending of the long switching shaft. The contact supports 3 pivotal on the switching shaft 2 are in any case so guided by the output contact ring 48 that in spite of described tolerance problems there is an exact control of the rollers 39 and 40 and thus actuation of the vacuum switches 27 and 28, in spite of their limited actuation strokes.
FIG. 3 shows a further embodiment of a load selector according to the invention. Here, unlike the above-described embodiment, the contact support 103 is not pivotal but instead is axially slidable. Inside the insulating cylinder 101 there is again a centered switching shaft 102 that carries a longitudinally slidable contact support 103. The longitudinal slidability is effected by means of a guide 104. In this system also there are two upright vacuum switches, of which only the front vacuum switch _ g _ 21457 PCT/EP99/02020 Transl. of WO 99/60588 105 is shown. In each plane there is also an annular array of fixed tap contacts 106 on the wall of the insulating cylinder 101 which are also engaged by a switching contact and an auxiliary contact of which in the figure only an upper contact part 107.1 and the respective lower contact part 107.2 are shown. Similarly there is again inside the insulating cylinder 101 an output contact ring 108 that is flanked by an upper output contact part 109.1 and a lower output contact part 109.2. The entire contact support is guided in this system by a roller 110 which rides on the surface of the output contact ring 108. The vacuum switches are controlled by two levers 115 and 116 which have on their free ends respective control rollers 113 and 114 that bear on a lower shaped control surface 111 or an upper shaped control surface 112 and thus actuate the actuating stems~of the vacuum switches, of which only the actuating stem 117 of the front illustrated vacuum switch 105 is shown.
FIG. 4 schematically shows the circuit that is formed by the load selector according to the invention. The electrical connections between the contacts 17 and 18 and the vacuum switches 27 and 28 and from there to the output contact 50 and thus to the output contact ring 48 are not shown in corresponding FIG. 1.
FIG. 5 shows a circuit where as shown in FIG. 2 the switch contact 17 is formed of two adjacent contact parts 17a and 17b. In this embodiment corresponding to FIG. 2 the electrical connections are also all that is shown. It is clear that the basic 21457 PCT/EP99/02020 Transl. of WO 99/60588 operation is not different, that it is achievable by the circuit of FIG. 4 of that of FIG. 5.
An exemplary switching sequence is shown in FIG. 6.
Thus a load selector with different switching steps is illustrated. Such.a load selector with varying switching steps is shown in principle in EP 0,160,125. Thus the average offset between the fixed tap contact connected to the primary winding and the two adjacent fixed step contacts is larger than the average distance between the remaining fixed tap contacts. This allows the load selector to be used also in transformers with high nominal voltage ratings; since they allow considerable continuous peak voltage to be handled. This reference also discloses particular fixed tap contacts that are variously formed for such a load selector.
In any case it is particularly advantageous that the fixed tap contacts 16 are not arcuate, as in the state of the art, so as to conform to the curvature of the insulating cylinder 1, but instead are straight as shown in FIG. 2. While according to the prior art the respective upper and lower contact parts 17.1, 18.1 and 17.2, 18.2 run continuously in the same track on the fixed arcuate tap contacts, the straight shape ensures that continuously other points of the surface of the fixed tap contacts 16 are engaged, reducing their wear.

Claims

claims:

1. A load selector for tapped transformers for interruption-free switching between taps of a control winding of a tapped transformer, the load selector having a housing formed as an insulating cylinder, fixed tap contacts connected with the taps being provided inside the insulating cylinder for each phase in a respective annular array lying in a horizontal plane, a rotatable switching shaft in the center of the insulating cylinder having for each array of fixed tap contacts an also rotatable contact support, each of the contact supports having at least two mechanical contacts that each are engageable with the fixed tap contacts of the respective array, at least one of the contacts of each contact support being directly connected with a first vacuum switch and least another of the contacts of each contact support being electrically connected via an overload resistor with a second vacuum switch, the other sides of the vacuum switches each being electrically connected with a load output, characterized in that all the contact supports (3) are movable on the switching shaft (2) independently of one another, and the two vacuum switches (27 and 29) are mounted upright on the contact support (3) such that their actuating stems (35 and 36) extend generally axially.

2. The load selector according to claim 1, characterized in that each of the contact supports (3) is pivotal about an axis on the switching shaft (2).

3. The load selector according to claim 1, characterized in that each of the contact supports (103) is axially slidable along the switching shaft (102).

4. The load selector according to one of claims 1 or 2, characterized in that each of the contacts (17 or 18) is formed of at least one upper contact part (17.1 or 18.1) and at least one lower contact part (17.2 or 18.2).

5. The load selector according to one of claims 1 through 4, characterized in that the fixed tap contacts (16) inside the insulating cylinder (1) extend horizontally nonparallel to an inner surface of the insulating cylinder (1), in particular in a straight line.

6. The load selector according to one of claims 1, 2, 4, or 5, characterized in that for each to be switched phase and thus for each horizontal planar array of tap contacts (16) there is on an inside surface of the insulating cylinder (1) a control ring (45) having an upper control surface (46) and a lower control surface (47), respective levers (37 and 38) are pivoted about respective pivots (43 and 44) on each contact support (3) for each of the two vacuum switches (27 or 28), and each lever (37 or 38) has a free end engaged with the actuating stem (35 or 36) of the respective vacuum switch (27 or 28) and has another end riding on one of the respective control surfaces (46 or 47) such that regardless of the shape of the respective control surface (46 or 47) the respective vacuum switch (27 or 28) is actuated.

7. The load selector according to one of claims 1, 2, 4, 5 and 6, characterized in that each load output is formed of an output contact ring (48) mounted concentrically on an inner surface of the insulating cylinder (1), has an outwardly extending connector element (49), and is contactable by a respective output contact (50) that is mounted on the respective contact support (3) and that is electrically connected with the vacuum switches (27 and 28) of the respective contact support (3).

8. The load selector according to one of claims 1, 2, 4, 5, 6, and 7 characterized in that each contact support (3) has two further rollers (55 and 56) that roll on respective sides of the respective output contact ring (48) such that the respective contact support (3) is guided.

9. The load selector according to one of claims 1, 2, 4, 5, 6, 7, and 8, characterized in that the control ring (45) and the output contact ring (48) of each phase are the same part.