DE1265290B - Diverter switch for step switches of step transformers - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

HOIf

German class: 21 d2-53 / 03

Number: 1265 290

File number: M 52987 VIII b / 21 d2

Filing date: May 25, 1962

Open date: April 4, 1968

The invention relates to a diverter switch for step switches of step transformers with main and switch contacts and several ohmic switch resistors connected in parallel between the main contacts and the respective tap of the transformer or tap selector an iron-closed choke coil is connected. The switching resistors can arbitrarily in the known circuits, such as the flag circuit, the pennant circuit or the Flag-pennant circuit must be switched.

In diverter switches of this type, increasing the switching capacity repeatedly causes difficulties. In most cases, with the change in the switching contacts, the design of the overall load switch must be used for this be changed. The main contacts of the Diverter switch divided into several parallel switching points, but with an even opening of all switching points cannot be reached mechanically and therefore the even distribution of the whole Load current could only be enforced by chaining the partial currents by means of choke coils. It is known for this to be between the main contacts and the respective tap of the transformer or the tap selector to switch an iron-closed choke coil. There is this current divider choke from two windings that influence each other inductively like a transformer, whereby the even distribution of the load current is to be enforced. With the same current The magnetization of both legs is at both contact points and windings connected in parallel equals zero. This in no way simplifies the circuit and construction of diverter switches and leads also not in every case to the desired success.

The object of the invention is to increase the switching capacity of diverter switches for tap changers of tap transformers to be achieved by simpler means. According to the invention happens this in that in a connection between the choke coil and one of the parallel-connected Switching resistors an ohmic magnetization resistor is connected, the one around a Much higher resistance than the switching resistors, and that the choke coil is only unsaturated in the area of the current zero crossing of the load current (switching choke).

This circuit of the choke coil according to the invention ensures that the arc at the main contact of the diverter switch is always extinguished, even in the event of an overload. A burnout of the diverter switch for tap changers
of step transformers

Applicant:

Reinhausen machine factory

Scheubeck brothers K. G.,

8400 Regensburg, Falkensteinstr. 8th

Named as inventor:

Dipl.-Ing. Wolfgang Breuer, 8400 Regensburg

Arc at the transition contact leads to the activation of the preselected phase when used the envisaged multiple parallel connection also certainly does not lead to any malfunction. Through the Choke coil and the ohmic magnetization resistance arise after the zero crossing at the Choke coil a voltage-free time, to facilitate the extinguishing of the arc and the current to be displaced by the resistance of the choke coil on the parallel switching resistors. It will so the recovery voltage at the disconnecting contact via a design of the choke coil kept close to zero for a certain period of time.

The arrangement according to the invention also makes it possible to use a diverter switch with single interruption of the main and transition contacts, which offers great advantages in terms of contact life especially at high currents, also taking into account increased requirements on the switching capacity.
The subject matter of the invention is to be explained in more detail using an exemplary embodiment and further advantages are highlighted.

F i g. 1 shows a circuit diagram of the diverter switch in flag circuit;

F i g. 2 shows simple oscillograms of the current and voltage curves when switching over the Diverter switch.

T is a part of a regulating transformer whose taps A and B are connected directly to the diverter switch for the sake of simplicity. A tap selector is normally connected between the control winding and the diverter switch.

809 537/237

The diverter switch has, in a known manner, parallel main contacts 1, 2 and 5, 6 and transfer contacts 3 and 4, which in the exemplary embodiment each have four interruption points. The transition resistors R _a and R _b are also divided into four parallel resistors .Ra ₁ and R _bl .

An iron-closed choke coil L _{a is connected} between the main contacts 1, 2 and the tap A , and a choke coil L _{b is} connected between the main contacts 5, 6 and the tap B. The choke coils L ₁₁ or L _b are connected to only one of the parallel resistors R ₁₁₁ or R _bl via a high-ohm magnetization resistor R ₁ or R " . The main and changeover contacts of the diverter switch are connected together to form a derivative M.

When the diverter switch is idle, one of the iron-closed inductors L _a or L _b always flows through it, so that its iron is saturated by the operating current of the transformer. The voltage drop across the inductor corresponds to the ohmic voltage drop and the leakage voltage drop and is therefore low. To explain the function of the choke coils, the exemplary embodiment according to FIG. 1 and the oscillograms according to FIG. 2 a changeover of the diverter switch from tapping A to tap B is considered:

In the rest position of the diverter switch, the main contacts 1 and 2 of the tap A are closed and current flows through the choke coil L _a. When the permanent main contact 1 opens, the load current is transferred to the parallel main contact 2. The switchover contact 3 then closes, and the main contact 2 opens at the same time. An arc is created at the main contact 2, which burns until the next current zero crossing.In the area of the current zero crossing, the inductor L _a intervenes in the switching process due to the voltage occurring during the magnetic reversal of the inductor.

From the oscillograms according to FIG. 2 this process can be seen in more detail. Shortly before the current zero crossing (time i ₂ ), the choke coil L _a comes out of saturation and thus becomes a very high resistance through which the current is displaced from the main contact 2 to the parallel switchover contact 3. The current at main contact 2 is thereby extinguished. The voltage recurring at the main contact 2 is almost zero as long as the choke coil L _{a is} unsaturated. The voltage which has applied the inductor L _a is determined by the voltage drop of the load current / g at Parällelwiderstand R _{a r} The magnetizing current of the choke coil L _B closes on the opposite the parallel resistor R ₀₁ very large resistance .R. ₁ However, since the magnetization current is negligibly small, the voltage drop at R _{1 is also} insignificant and thus the return voltage at the main contact 2 is practically zero.

As can be seen from the oscillograms in FIG. 2, the iron of the choke coil L _{a is} in saturation from time t ₃ , the self-induction voltage U ₁ breaks down to the stray voltage and the ohmic voltage drop. The current i " through the choke coil is limited by the magnetization resistor R _1. The recovery voltage u _w at the main contact 2 thus corresponds to that in FIG. 2 curve shown schematically. The voltage is zero from time t ₂ to t _a and corresponds from time t ₃ to the voltage drop of the operating current i _z at the switching resistor R _a . The choke coil must therefore be chosen so that the voltage-free time at the main contact 2 is definitely sufficient to avoid re-ignition at this contact.

The further switching sequence of the diverter switch corresponds to that of a normal flag switching. Of the Over-switch contact 4 closes and at the same time switch-over contact 3 opens. To facilitate deletion of the arc, the switch contacts 3, 4 are each divided into four parallel current paths. When the switchover contact 4 closes, an equalizing current is generated, which is equal to the operating current superimposed.

The current at the transition contact 3 goes out in the following zero crossing, the voltage drop across the transition resistors R _b together with the step voltage results in the recovery voltage at the transition contact 3. The switchover is terminated by switching on the main contact 5 and then the permanent main contact 6 If a return ignition occurs, the arc burns at this contact when the main contacts 5 and 6 are switched on. After switching on the main cort clock 5, the operating current is taken over by the tap B. Since the arc at the transition contact 3 is still burning at this point in time, an equalizing current is created, caused by the step voltage and limited by the transition resistance. By dividing the transition resistors into several parallel branches, this equalizing current per contact point can be reduced by the transition contact 3 to such an extent that reliable extinction is guaranteed at the individual points.

Claims (1)

Claim: Diverter switch for step switches of step transformers with main and over-holding contacts and several ohmic over-switching resistors connected in parallel, in which an iron-closed choke coil is connected between the main contacts and the respective tap tap of the transformer or the tap selector, characterized in that in a connection between the choke coil (L _a or . L _b ) and one of the transition resistors (R _at or R _b j) connected in _{parallel, an ohmic magnetization resistor (A 1} or R. ₂ ) is connected, which has a resistance value that is many times higher than the transition resistances (R _a or R _b ) and that the choke coil (L ₀ or L ₁ ,) is only unsaturated in the area of the zero crossing of the load current (switching choke). Considered publications:
German patent specifications No. 582 439, 822 572 » 960 559; Austrian patent Nf. 196 974;
Magazine "Frequency", Vol. 1/1947, No. 1, p. 2 to 15, 1 sheet of drawings 809 537/237 3.68 © Bundesdruckerei Berlin