EP0763835A2 - Tap selector - Google Patents

Abstract

The step selector has two-part selector contacts (1,2...), each consisting of a fixed part (1a,2a..) and a corresp. moving part (1b,2b..). Each fixed contact part is electrically connected to an output winding line of a step coil of a step transformer. All moving contacts are connected to a conventional load changeover switch for switching between any two selector contacts. All movable contact parts are separately driven or activated so that they can be electrically connected to the corresp. fixed contact parts individually and independently from each other.

Description

The invention relates to a tap selector of a tap changer for a tap changer.

Step switches have been known for many years in order to be able to adjust the voltage, active and reactive power of electrical networks by changing the gear ratio under load.
The introduction of on-load tap-changers considerably improved the operating options for electrical networks, so that today, for example, in Germany 96% of power transformers over 10 MVA are equipped with on-load tap-changers.
With the exception of the USA and partly the former Soviet Union, tap changers worldwide operate according to the principle of high-resistance switching.
Basically, such tap changers consist of the tap selector and the diverter switch and work in two steps. The tap adjacent to the live tap is pre-selected by the tap selector. Then the current is switched by the diverter switch from the current-carrying to the preselected tap. The step change is usually effected by a motor drive, which actuates the selector via a Maltese transmission and at the same time tensions a spring energy store, which in turn drives the diverter switch abruptly after tripping.

In Fig. 1 such a known tap changer according to the prior art is shown schematically.
A tap selector W consists of fixed tap contacts 1 ... 6, which are electrically connected to the individual winding leads of the tap transformer and are usually arranged in two planes per phase in the wall of an insulating material cylinder, such that the even numbered and in the odd-numbered step contacts are arranged on the other level. The tap selector W also consists of two movable selector contacts W1, W2, which are usually rotatably arranged in the interior of the insulating material cylinder and can connect the fixed tap contacts 1 ... 6. The two movable selector contacts of each phase W1, W2 lead to the diverter switch LU, by means of which the changeover from the current-carrying to the newly selected step contact takes place.
In Fig. 1a, the switching principle of such a known tap changer is shown: Each time the load is switched, the tap adjacent to the current-carrying tap is preselected, then the current is switched by the load switch from the current-carrying tap to the preselected tap.

If there are several circuits, both selector contacts W1 and W2 are moved alternately; when switching from 2 to 3, W1 leaves the fixed contact 1 and contacts the adjacent contact 3, during the subsequent switchover W2 leaves the previous fixed contact 2 and contacts the adjacent fixed contact 4, etc.
Depending on the type and construction, the process of each load changeover takes about 40 to 60 ms. The load changeover that has been initiated inevitably takes place after the spring energy storage device has been triggered, with the switching resistors R being loaded for about 20 to 30 ms. The total time of the tap changer from the activation of the motor drive to the end of the load changeover is, depending on the design, about 3 to 6 seconds.

For certain control tasks, it is necessary to implement larger tapping changes quickly, ie to switch with the tap changer between taps further apart, for example the fixed tap contacts 1 and 6. This is only possible with the known tap changers in such a way that, since in principle and due to their function, they can only switch between adjacent taps, all taps in between must be run through as separate switchovers, as can be seen from FIG. 1a.
This is too slow for many applications.

The object of the invention is to provide a tap selector for a tap changer in which any switching between freely selectable, not necessarily adjacent, winding taps is possible.

This object is achieved by the invention.
The tap selector according to the invention allows switching between any winding taps without the intermediate taps having to be run through and without, as is customary in the prior art, adding up the times for several individual load switches.

The invention will be explained in more detail below with reference to drawings.
Fig. 2 shows a first embodiment of a tap selector according to the invention.
The selector contacts each consist of two parts, a fixed contact part 1a, 2a, ... and a corresponding, separately operable, movable contact part 1b, 2b .... The fixed contact parts 1a, 2a, ... are U per phase , V, W arranged in two planes A, B in the wall of the insulating cylinder Z; the corresponding movable contact parts 1b, 2b, ... are located inside the insulating cylinder Z on a support T.

The movable contact parts 1b, 2b, ... are designed such that they extend a contact tongue or the like when actuated and this comes into electrical connection with the corresponding fixed contact part, such that the electrical connection between the two parts of the corresponding Selector contact and thus for the corresponding winding rejection of the step winding is produced.
The movable contact pieces, which, as already explained, can be actuated separately and independently of one another in any order, can be actuated, for example, hydraulically or by electromagnetic means.
Each movable contact part of each phase is electrically connected to both sides of the diverter switch, not shown, such that the diverter switch can switch between any winding taps.
What is essential to the tap selector according to the invention is the complete decoupling of the tap selector and diverter switch on the one hand and the possibility of arbitrary tap preselection on the other.

When dimensioning the associated diverter switch, it should only be taken into account that not only, as in the prior art, a step voltage, i.e. the voltage between adjacent taps of the step winding is present, but possibly a multiple thereof.

3 and 3a show a schematic representation of the corresponding switching scheme and a possible direct switching sequence between non-adjacent tap taps with the tap selector according to the invention.

Fig. 4 shows a second embodiment of the invention, in which, in contrast to the design shown so far, the contacts are not arranged in horizontal planes, but in vertical assignment. Here, six vertical areas are provided on the circumference of the insulating cylinder Z, the fixed contact parts 1a, 2a,... Being arranged in each case in two — preferably adjacent — areas for each phase. Corresponding to this, the movable contact parts are in turn inside the insulating cylinder Z on a carrier T.
Operation and function do not change as a result of this changed design, but this arrangement has certain advantages with regard to contact rejection, ie the routing of lines from the movable contact parts to the diverter switch.

Claims (1)

Step selector of a step switch for a step transformer with the following features: - It has two-part selector contacts (1, 2, ..., n) - Each currency contact (1, 2, ..., n) consists of a fixed contact part (1a, 2a, ...) and a corresponding movable contact part (1b, 2b, ...) - Each fixed contact part (1a, 2a, ...) is electrically connected to a winding rejection of a step winding of the step transformer - All movable contact parts (1b, 2b, ...) are electrically connected to the load switch known per se for switching between any two selector contacts (1, 2, ...) - All movable contact parts (1b, 2b, ...) are separately controllable, ie operable, in such a way that they can be electrically connected individually, independently of one another and in any order to the corresponding fixed contact parts.

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