Switching system with preselector

Abstract

The invention relates to a step switch, comprising a pre-selector and a fine selector. The invention is characterized in that the step switch has a connection (36) between the pre-selector and the fine selector (18), at least one coupling switch (38) being arranged in said connection. A pre-selector can be switched in a largely gas-free manner by means of said switchable connection with the aid of the fine selector.

Claims

1. A tap changer comprising: a preselector having a movable preselector switching element and two preselector switch contacts contactable by the movable preselector switching element; a fine selector having a movable fine-selector switching element and at least two fine-selector switch contacts contactable by the movable fine-selector switching element; at least one coupling switch between the preselector and the fine selector and having a movable coupling-switch switching element and a coupling-switch contact, the movable coupling-switch switching element or the coupling-switch contact being connected to a load output, the coupling-switch switching element being connected to the movable preselector switching element so that, when the movable coupling-switch switching element engages the coupling-switch contact, the movable preselector switching element disengages from the preselector contacts and is set to an unconnected neutral setting, and, when the movable preselector switching element contacts any of the preselector contacts, the movable coupling-switch contact element disengages from the coupling-switch contact.

2. The tap changer according to claim 1, further comprising: a transmission for actuating the coupling switch and between the load changeover switch and fine selector.

3. The tap changer according to claim 1, wherein the fine selector contacts are snap switches or a vacuum interrupter.

4. The tap changer according to claim 1 wherein the tap changer is a rotary switch.

5. The tap changer according to claim 1, wherein the fine selector is a load selector.

6. The tap changer according to claim 1, wherein the preselector is as a reverser.

7. A control transformer with at least one primary winding and control winding, the transformer comprising a tap changer according to claim 1, wherein the control winding has a plurality of taps connectable by the fine selector and the preselector connects the control winding in a desired polarity with the primary winding.

8. A method of switching a preselector in a tap changer according to claim 1, the method comprising the following sequence of steps: a) moving the fine selector to the end position of the preselector at the control winding, b) switching the coupling switch from an open normal setting to a closed switching setting, c) switching the preselector to a non-contacting neutral setting, d) switching the fine selector through by the taps of the control winding to the opposite end position at the control winding, e) switching the preselector to the end position at the control winding, at which the fine selector in contact, and f) opening the coupling contact to its normal setting.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is now described by example on the basis of the schematic drawings, in which:

(2) FIG. 1 shows a circuit diagram of a tap changer of a control transformer with a primary winding and control winding, which tap changer comprises a preselector, fine selector, load changeover switch and coupling switch, and

(3) FIGS. 2a-f show a series of circuit diagrams for clarification of the switching process of the preselector with the help of the fine selector, for example in a control transformer of FIG. 1.

SPECIFIC DESCRIPTION OF THE INVENTION

(4) The control transformer 10 comprises a primary winding 12 and a control winding 14 with a plurality of taps 16. A tap changer 17 consisting of a preselector 20 and a fine selector 18 is arranged in the control transformer 10. The fine selector 18 in turn consists of fine selector contacts 32, 34 and a load changeover switch 24 that switches between the fine selector contacts 32, 34. The preselector 20 is constructed as a reverser. The preselector 20 connects the control winding 14 with the primary winding 12 in desired polarity and the fine selector 18 preselects, by the fine selector contacts 32, 34, the taps 16 of the control winding 14 to be connected, in which case switching between the fine selector contacts 32, 34 is effected in this embodiment by the load changeover switch 24. The primary winding 12 is connected with the switching element 22 of the preselector 20, and the switch contacts 21, 23 thereof are connected with the ends of the control winding 14. The switching element 22 of the preselector 20 thus selectably connects one of the two ends of the control winding with the primary winding 12 by the switch contacts 21, 23 or it remains in a non-contacting neutral setting, as shown in FIGS. 2c and 2d.

(5) The fine selector 18 is connected with a load diverter 28 by the load changeover switch 24. The load changeover switch 24 comprises a slide switch that contacts the two fine selector contacts 32, 34 in alternation with a short transition phase and with utilization of switching resistances 30 of the load changeover switch 24. The load changeover switch 24 thus includes two switching resistances 30, each of which is connected with a respective one of the fine selector contacts 32, 34. In this way the slide switch element 26 moves across four contacts of the load changeover switch 24, in which case there is switching from one tap 16 to the next tap 16 of the control winding 14 with interposition of the switching resistances 30. Before the actual switching process in the load changeover switch 24, the taps to be connected are preselected in voltage-free manner by the fine selector contacts 32, 34. Thus, with each switching process the slide switch element 26 moves from the illustrated right-hand end position in the load changeover switch 24 to the lefthand end position (dashed-line illustration) and vice versa. Other components and switching sequences can also be used in the load changeover switch 24, for example vacuum interrupters with auxiliary switches. Moreover, the tap changer 17 can also be constructed as a so-called load selector in which the fine selector 18 consists of the load changeover switch 24 and the fine selector contacts 32, 34. Preselection of the tap 16 to be connected and the load switching process are here carried out in one step.

(6) According to the invention the fine selector 18 is now connected by an electrical connection 36 with the preselector (reverser) 20, preferably with the switching element 22 thereof. A coupling switch 38, by which the connection between the load diverter 28 of the load changeover switch 24 and the primary winding 12 can be interrupted, is arranged in this connection 36. The switching element 40 of the coupling switch 38 is preferably coupled with the switching element 22 of the reverser 20 by a mechanical or electrical coupling 42, whereby actuation thereof can be synchronized. The switching element can be constructed as a vacuum interrupter or snap contact. Switching of the reverser in a tap changer 17 as described above is explained in the following FIGS. 2a-2f.

(7) Identical or functionally equivalent parts are provided in the figures with the same reference numerals. The load changeover switch 24 is illustrated only very schematically in the schematic drawing sequences of FIGS. 2a-2f.

(8) FIG. 2a shows the normal operating setting of the tap changer 17, in which the coupling switch 18 is opened, so that the voltage at the load diverter 28 of the load changeover switch 24 corresponds with the voltage corresponding with the tap 16 of the control winding 14 and the corresponding voltage component of the primary winding 12.

(9) For the switching of the preselector 20, i.e. for switching over the polarization of the control winding 14, the coupling switch 38 is closed (FIG. 2b) when the fine selector 18 lies on the winding tap 16 that corresponds with the contact position of the reverser 20, of the control winding 14. The switching element 22 of the reverser 20 is now switched to a non-contacting neutral position as shown in FIG. 2c. The switching elements 40 of the coupling switch 38 and the switching element 22 of the reverser 20 can be coupled together so that the opening and closing of the switching elements takes place in coupled manner, i.e. with constrained synchronisation. In a preferred form of embodiment the actuation can take place by a transmission (not illustrated here) arranged between load changeover switch and selector. Moreover, it is possible for the actuation to be derived directly from the preselector 20. In this way faulty operation of the corresponding switching elements is excluded. In the switching phase illustrated in FIG. 2c the control winding 14 is now connected solely by the fine selector 18 and load changeover switch 24 with the primary winding 12. The fine selector 18 now moves, by means of the fine selector contact 32, 34 in conjunction with actuation of the load changeover switch 24, to the other end position of the control winding 14 as illustrated in FIG. 2d. In that case, the load changeover switch 24 always switches back and forth between the two fine selector contacts 32, 34 after the fine selector has preselected the next tap. When the fine selector has switched through to the other end of the control winding 14, the switching element 22 of the reverser 20 is in turn switched into the contact setting with respect to the other end of the control winding 14, at which the fine selector 18 and the load changeover switch 24 are present. Since the reverser 20, primary winding 12 and fine selector 18 together with the load changeover switch 24 lie by the closed coupling contact 38 at the same voltage level, this switching process of the reverser 20 also takes place in potential-free manner, i.e. without generating an arc and thus free of gas. After switching of the reverser according to FIG. 2e, the coupling switch 38 is now re-opened as illustrated in FIG. 2f. The control transformer 10 has now again reached its normal operating position; fine selector.

(10) The invention is not limited to the illustrated embodiments, but can be varied within the scope of protection of the following claims. In that regard, instead of mechanical switching contacts such as, for example, vacuum interrupters, it is possible to use semiconductor switching elements such as, for example, IGBTs. These semiconductor switching elements can be used in the fine selector 18, load changeover switch 24, preselector 20 and the fine selector contacts 32, 34 for the switching.