DE628749C - Electrical switch with electrodes moved in resistance fluid - Google Patents

Description

Switches with electrolytic switching fluid, in which case the power is interrupted with the movement of the electrodes, there is an increasing fluid resistance in the switch-off Circuit is switched on, are known. In one of these known switches, a hollow electrode is made from Liquid pulled out, from which jets of liquid then run out, so that in the last part of the switching movement the resistance increases rapidly by lengthening the liquid columns. All of these switches are only suitable for switching off relatively small currents, while when you are using them higher currents, an arc at any point during the shutdown process is ignited.

The invention relates to a switch with resistance fluid, which is used for interruption very high currents at high voltages is suitable, i.e. a high-performance switch. The invention consists in that in the first part of the switch-off process, the change in resistance is essentially due Area reduction, in the second part essentially by changing the length of the active one Resistance body is generated and the electrode surfaces are dimensioned and arranged in this way are that during the switch-off movement and especially during the transition from the increase in resistance through Area reduction to that by increasing length in no spatial element the boiling point of the liquid is exceeded.

On the one hand, this results in a rapid increase in resistance with a moderate electrode stroke achieved, on the other hand, there is the risk of evaporation of the liquid and thus an arcing eliminated even when switching off large powers.

The principle on which the invention is based can be mathematically as follows grasp: ..

) fS.dt. <c- (DsP- "o

(x)

"O

It means:
j

= Current density in A / cm ² ,

5 * = specific resistance of the liquid in ohms / cm,

t _a = switch-off time,

c = specific heat of the liquid W

^rr see

D _Sp = boiling point of the liquid at

Pressure p, D ₀ = temperature of the liquid at time t = o ..

If there is a hemispherical electrode, for example, in any liquid, then according to Fig. 1 the resistance is r, provided that the radius J _{0 of} the hemisphere

$ 62874

in relation to the vessel dimensions is small, given approximately by the following formula:

If one now reduces the radius of the hemisphere, which is equivalent to 'pulling an electrode out of the liquid, one recognizes that the resistance finally becomes infinitely large for S ₀ = O'. If there is a constant voltage U ₁ at this fluid resistance as shown in FIG

Oq.

(3)

The current density / is given by the quotient of the current and the surface F of the hemisphere and is accordingly

2 π US ₀

SS _n

= i (4)

From (4) it can be seen that ¹ in the last part of the switch-off process, ie for ever smaller spherical surfaces, the current density: tends towards infinity.

The course of residual current, area and current density is shown in Fig. 2 as a function of · S ₀ . It is essential that this consideration applies not only to hemispherical electrodes, but to electrodes of any shape. The same phenomenon occurs - if the positive and negative electrode ¹ emersion simultaneously from the switching liquid 'and thus the surfaces of the electrode and ·: the. Counter electrode the same during the entire switch-off process; large "are". The cause is the expansion of the current lines between the electrodes in the liquid.

The further inventive idea to overcome this principle; difficulty is now that the cross-sectional reduction of the active liquid volume is only driven so far until · the current density passes through. Equation (i), prescribed; Has reached the limit. From this point on, the cross-section is no longer further decreased, but the resistance increased in other ways. This can e.g. B. take place in that in the last switching phase the movable. Electrode in liquid with high resistivity, immersed or that effective during the last phase Liquid has a positive temperature coefficient. You can use their liquids of = different specific gravity sö> layers one on top of the other; that 'the specific Resistance with; as the switch-off process progresses.

Another measure is that the movable electrode is made hollow, provided with a lower opening and filled with liquid. After the metal surface of this electrode has been separated from the liquid level, the resistance of the structure is given by the liquid jet emerging from the hollow electrode. The lengthening of this liquid jet leads to any increase in resistance . without further compression of electricity. Instead of the freely flowing jet, a columnar active liquid body can also be shielded from the liquid body by an insulating jacket in the last switching phase, which also results in a steadily increasing increase in resistance without increasing the current density.

The conditional equation (1) can be fulfilled particularly easily if the liquid puts under increased pressure, as this increases their boiling point and detachment of the liquid from the movable electrode is avoided. With hindsight In order to detach the liquid, it is useful to give the movable electrode a shape which swirls the liquid avoids, e.g. B. teardrop shape.

Two possible embodiments of the invention 9 " application are shown in Figs. 3, 4, 5 and 6.

In Fig. 3, χ denotes the stationary liquid container, 2. the movable, drop-shaped electrode, 3 a switch blade which, in the switched-on position, engages in the main contacts 4 and is firmly connected to the switching rod 5. 6 ' is a ring made of insulating material to avoid electrical discharge along the surface of the liquid 7, a so-called ion barrier. At its lower end, the movable electrode 2 has a space 8 which fills with the switching fluid when it is immersed.

In Fig. 4 · the switch is shown shortly before the end of the switch-off process. The connection between the movable electrode 2 and DFEM liquid level 7 is just still given by the liquid jet 9 ^1, whose resistance increases with increasing length of this beam. The liquid can flow out of the space 8 unhindered, since the air has free access through the openings 10.

The mode of operation of the arrangement is now as follows:

When moving. Shift rod 5 according to at the top · first the switch blades separate 3 and the contacts ^. This will the current is forced to flow through: the liquid. The distance between

of the movable electrode and the liquid container is still very much at this point small and thus the resistance is correspondingly low. The movement must be carried out in such a way that that no switching fire occurs when the main contacts are disconnected. With the further lifting of the electrode 2, its wetted area is reduced, and thus the resistance increases. It also increases the length of the streamlines. At the moment, since the lower edge of the movable electrode is the Liquid level is reached, the change in resistance, which was previously in the essentially through a reduction in area

* 5 was caused into a change in resistance implemented by increasing the length of the active resistor body. This State is shown in Fig. 4. The volume of the liquid in the space 8 must be so be dimensioned so that the liquid path 9 reaches such a resistance at the end, that the interruption of the residual current takes place without interference. Experience shows that currents below 5 amps in general can be switched off without interference.

A particular advantage of this arrangement can be seen in the fact that the liquid path 9 can be loaded relatively high because the active fluid is constantly renewed and the heat dissipates. Particularly useful Ratios are achieved in this respect if the liquid is allowed to flow out under increased pressure. To the To hold the liquid jet together, a jet regulator known per se can be used will. It can also be the flow of liquid emerging from the movable electrode be fed into an insulating tube, which is attached to the electrode.

Instead of a single liquid path 9, several liquid jets can be arranged in such a way that with falling liquid level in space 8 these jets one after the other to dry up

+ S to be brought.

In Fig. S and 6 11 means the liquid container, 12 the movable outer, 13 the movable inner electrode. 14 is an insulating cylinder with openings 15. When switching off, the outer electrode 12 moves upwards and thereby the resistance mainly by reducing the Cross-section enlarged. At the moment when the cover 16 is on the collar 17 of the inner When electrode 13 hits, this inner electrode (see Fig. 6) is removed from the insulating tube pulled out. This results in a change in resistance that remains practically the same Current density essentially due to the extension of the resistor body.

In order to be able to switch on without interference, it is generally advisable to use the main contact close first. For this purpose the main contact 3-4 (see e.g. Fig. 3) is separated from the liquid electrode arranged and closed when switching on before immersing the movable electrode 2.

To safely under- the last residual current. to be able to break, it is advantageous as the uppermost liquid layer in per se known Way to use one made of an insulating liquid, by virtue of its smaller one specific weight floats on the switching fluid.

To avoid arcing after separating the movable electrode from the To safely prevent the surface of the liquid, it is used as a fixed electrode Liquid container designed according to the figure with a widening edge, so that with increasing switch-off movement, the distance between the electrodes increases along the liquid level.

Claims (11)

85 claims: 1. Electrical switch with in resistance fluid moving electrodes, between which when the power is interrupted a resistance increasing with the electrode movement is switched on, characterized in that im first part of the switch-off process the change in resistance essentially by reducing the area, in the second part essentially by changing the length of the active resistance body is generated and the electrode surfaces in such a way are dimensioned and arranged that during the disconnection movement and in particular at the transition from the increase in resistance by reducing the area to that by increasing the length the boiling point is not exceeded in any spatial element of the liquid will. 2. Switch to. Claim 1, characterized in that from the movable, hollow electrode filled with switching fluid after it has been separated from the fluid fluid level jets of fluid leak out. 3. Switch according to claim 2, characterized in that the from the movable The liquid jet emerging from the electrode is guided in an insulating tube. 4. Switch according to claim 1, characterized in that the active body of liquid during the last part of the switch-off movement through an insulating jacket surrounding the movable electrode is shielded on columnar form. 5 · Switch according to claim ι, characterized characterized in that, as the interruption process progresses, the movable electrode in liquid with high specific Resistance dips. 6. Switch according to claim i, characterized in that with advancing Interrupting the moving electrode in fluids with positive Temperature coefficient immersed. 7. Switch according to claim 1, characterized in that the switching off movement the distance between the electrodes along the liquid level is increased. 8. Switch according to claim i, characterized in that the liquid level is pierced by concentric * isolation rings, which act as ion barriers. 9. Switch according to claim 1, characterized in that .the liquid is placed under increased pressure.
, 10. Switch according to claim 1, characterized in that several liquids of different specific gravity are stacked so that the specific resistance of the Layers increases as the switch-off process progresses. 11. Switch according to claim 10, characterized characterized in that the last liquid layer consists of an insulating liquid. 12, switch according to claim 1, characterized by a main contact moved separately from the liquid electrode, which is activated before the Immersion of the liquid electrode is closed. 1 sheet of drawings