HK1173553B - Tap changer with polarity switch for control transformer - Google Patents

Description

The invention relates to a pre-selectored step switch with a polarisation circuit for continuous control on a control transformer.

DE 19 42 567 A describes a step switch with a pre-selector for the selectable sequential circuit of steps of the step winding to the corresponding main winding of a step transformer, where the step switch's inverter contacts are formed as switching contacts.

In such step switches, the step winding of the corresponding step transformer is briefly galvanically separated from the main winding during the operation of the pre-selector. It assumes a potential resulting from the voltages of the adjacent windings and the coupling capacities to these winding or grounded parts. The resulting differential voltages demand the switching lines of the opening switch contacts and can, among other things, lead to unacceptable discharge phenomena on the pre-selector.

DE 32 24 860 A describes a similar arrangement on a step switch, where, as shown in Figure 1b, a pulley resistor is also directed to the centre of the step winding.

The DE 195 42 880 C1 shows a polarisation switch particularly suitable for such a short-term orientation of the centre of the step winding.

JP 55-133515 A and DD 47965 B1 show that a step switch with a polarity switch for continuous control is equipped with a control transformer with a voltage-dependent resistor to protect against overvoltages when the control is switched.

DE 24 21 728 A1 describes a step switch with a pre-switch and a polarisation circuit, whereby voltage-dependent resistors are placed above the control winding in combination with oil spark lines to protect against overvoltages when switching the pre-switch.

Finally, it is already known from DE 11 65 154 A that, in the case of a step switch equipped with a pre-switch, the centre of the control winding is connected to the load line by means of a voltage-dependent resistor to protect against overvoltages when the pre-switch is switched and that voltage-dependent resistors are provided in parallel with the control winding terminals.

In summary, the state of the art in the case of pre-selectored step switches with a polarity switch can be summarised as follows: a polarity resistance is provided between the centre of the step winding and the load line, which is connected to the load line permanently or only briefly during the switch, before the pre-selector operation begins, by means of a polarity switch.

The disadvantage of these known solutions is that this polarisation circuit switches off the undesirable capacitive current from the pre-selector, i.e. it is interrupted; light arcs are inevitable. These light arcs cause a gas formation. This is undesirable for many applications, for example in ultra-high voltage applications.

The purpose of the invention is therefore to provide a step switch with an improved polarization circuit, which results in a significantly reduced arc formation at the predecessor.

This task is solved by a step-change of the type mentioned at the outset, with the characteristics of subsidiary claims 1 or 2.

The general idea of the invention, which applies to both embodiments in the related claims, is to provide for two separate polishing resistances connected at the beginning and end of the step winding.

The essential advantage of both embodiments of the invention is that the two polarising resistors provided for in the invention provide a bypass for the capacitive current; the capacitive current commutates from one side to the other - it does not have to be switched off, i.e. interrupted, by the predecessor, contrary to the state of the art.

The invention is further described below by means of drawings showing: Figure 1a state of the art arrangementFigure 2a first embodiment of the invention according to the patent claimFigure 3a second embodiment of the invention according to the patent claim 2.

The switch 3 initially selects without power before a switch the new winding connection of the stage 2 winding to be switched to. The switch itself is made by a known load switch 4 of the stage transformer, which will not be discussed in detail here. Furthermore, the stage switch shows a pre-selector 5 connected to the stage winding connection to the start area of the control or at the end of the stage 2 winding at the end of the stage 2 winding. The switch itself consists of a short voltage switch, which can be connected directly to the middle of the stage 9 or 9 winding.

The constant actuation of the polarising resistor 7 - although only needed during switching - causes additional transformer losses, so in many cases a polarising switch 8 is inserted into the polarising circuit.

Figure 2 shows a first embodiment of the invention; identical components are provided with identical reference marks. In contrast to the state of the art, the invention provides for a first polarising resistor 11 at the beginning of step 10 of the step 2 winding, which is connected to the load line by means of a first polarising switch 12; furthermore, the invention provides for a second polarising resistor 14 at the end of step 13 of the step 2 winding, which is connected to the load line 9 via a second polarising switch 15; the two polarising switches 12, 15 are only briefly switched on before the start of the operation of the precursor 5 so that only briefly the beginning of step 10 and the end of step 13 of the step 2 winding are directed to a defined potential.

Figure 3 shows a second embodiment of the invention in which no polarity switches are provided for; rather, a first polarity resistor 11 is fixed and permanently applied at the beginning of step 10 of step 2 and a second polarity resistor 14 at the end of step 13 of step 2.

Finally, it is a matter of discretion within the framework of the invention which of the two variants to choose.

In particular, it is advantageous to design the polarising resistors 11, 14 asymmetrically in both embodiments, so that the specific polarising conditions at the respective transformer can be easily adjusted or compared.

Claims (3)

1. Tap changer, which is provided with a preselector, with a polarity circuit for uninterrupted regulation at a regulating transformer, wherein the regulating transformer comprises one or more main windings (1) and a tap winding (2), wherein the tap changer is switchable between different winding taps of a tap winding (2), which are each connectible with a load shunt (9), and wherein a polarity circuit is provided in such a manner that the tap winding (2) during switching over from one winding tap to another winding tap is connectible with the load shunt (9), characterised in that provided at the start (10) of the tap winding (2) is a first polarity resistance (11) which is connected with the load shunt (9) by way of a first polarity switch (12) and that provided at the end (13) of the tap winding (2) is a second polarity resistance (14) which in turn is connected with the load shunt (9) by way of a second polarity switch (15).
2. Tap changer, which is provided with a preselector, with a polarity circuit for uninterrupted regulation at a regulating transformer, wherein the regulating transformer comprises one or more main windings (1) and a tap winding (2), wherein the tap changer is switchable between different winding taps of a tap winding (2), which are each connectible with a load shunt (9), and wherein a polarity circuit is provided in such a manner that the tap winding (2) during switching over from one winding tap to another winding tap is connectible with the load shunt (9), characterised in that provided at the start (10) of the tap winding (2) is a first polarity resistance (11) which is connected with the load shunt (9) and that provided at the end (13) of the tap winding (2) is a second polarity resistance (14) which in turn is connected with the load shunt (9).
3. Tap changer according to claim 1 or. 2, characterised in that the two polarity resistances (11, 14) have different electrical values.