US1985928A - Load-change-over switch for step transformers - Google Patents

Description

5. JANSEN Jan. 1, 1935.

SFORMERS LOAD CHANGE OVER SWITCH FOR STEP TRAN Filecl Jan. 25, 1933 2 Sheets-Sheet l Bernhard Jansen INVENTOR ATTORNEY.

B. JANSEN Jan. 1, 1935.

LOAD CHANGE OVER SWITCH FOR STEP TRANSFORMERS Filed Jan. 25, 1933 2 Sheets-Sheet 2 Ill/I21 lmiv INVENTOR Bernhard Jansen ATTORNEY Patented Jan. 1, 1935 PATENT OFFICE DOAD-CHANGE-OVER SWITCH FOR STEP TRANSFORMERS Bernhard Jansen, Begensburg, Germany Application January 25, 1933, Serial No. 653,401 In y January 26, 1932 6 Claims.

--Step transformers are known in which the electric current is switched over from one tap to another, during' operation of the transformer, by means oi! step switch devices which for a short time interpose a resistance between the two taps to be connected.

For this purpose ohmic as well as inductive resistances are usedwhich, as a general rule, have but little variable resistance. As a conse- 'quence, current and voltage fluctuations occur when the resistances are switched on or off necessarily producing spark discharge. The spark discharges eventually damage the switch contacts and in the case of oil switches, cause the oil to deteriorate.

According to the present'invention spark discharge at the switch contacts may be wholly avoided if instead of constant resistances, variable resistance means are used, e. g., electrolytic liquids.

It is a known fact that the resistance of 'electrolytic liquids of alternating current not only depends upon their chemical composition and concentration, but also particularly upon the greatness of the surface of current transgression, the length or e path of the current in the liquid and the g neration of heat therein. Inasmuch as electrolytic liquids may be chosen according to their most favorable chemical and physical properties, and the surface of current transgression and the current path may be varied .continuously by moving the contacts to be connected or interrupted, it is possible to change the resistance between the contacts -i'rom maximum to zero. The degree of the desired (or admissible) heat generation may be influenced by the switching speed. Thus, it is, possible to close or break contacts without causing sudden fluctuations of the current or voltage. It is of course true that electrolytic liquids can produce this effect raultlessly between certain current and voltage limits only (20,000 amperes and 4,000 volts) but those limits sumce fully for purposes of step transformers. The current limit is hardly reached even in the case of lowest voltages. The voltage limit, on the other hand, is. suflicient because instep-switches the switch voltage encountered, like the step voltage, represents but a fraction of the entire working voltage. (In the case of 150,000 volts working voltage and 3% steps-a voltage of is found.) j

One embodiment of the present invention utilizes an electrolytic resistance as illustrated in a the accompanying drawings, in which Fig. 1 shows a two-contact switch;

Fig. 2 shows a transformer having four taps;

Fig. 3 shows an embodiment of a circular tap changer comprising two taps;

Fig. 4 shows an embodiment of a three-tap changer.

In Fig. 1 a simple load transfer-switch is shown comprising two taps. The switch comprises two vessels Ga, Gb, each containing an electrolytic fluid Y. Contacts Ta and Tb, are immersed'in the vessels Ga, Gb, respectively, and are connected to taps 1 and 2 of the secondary S. Two contact pins A, B are carried by connecting rod K and adapted to cooperate with contacts Ta and Tb. Connecting rod K is pivoted at X at which point the lead-off line C branches oil. In the position shown, lead-oil line C is connected to tap 1 of the secondary S through contact pin A and contact Ta. If lead-off line C is to be connected with tap 2 of the transformer S, the connecting rod K is turned in the direction of the arrow. When rod K is turned, contact pin A is removed from contact Ta, the current flow from tap 1 to contact Ta and contact pin A being maintained, however, owing to the electrolytic fluid Y, ofiering but little resistance. -While contact pin A is raised, contact pin B is lowered entering the electrolytic liquid contained in vessel Gb. When contact pin B immerses in the electrolyte of the vessel Gb a weak current flows, against a very high initial resistance, from tap 1 over contact Ta, pin A, rod K, pin B, contact Tb to tap 2 of the secondary S. This current has equalizing effect while at the same time current supplied from tap 2 flows through contact Tb, pin B and lead-oil line C. In the operation so far described pin B moved through the electrolyte only and did not yet make contact with contact Tb. While contact pin B continues to approach contact Tb and pin A is further removed from contact Ta, a gradual shift of the current flow takes place in such manner that tap 1 is entirely out out and current delivered from tap 2 only. The switching step is concluded when pin A is withdrawn from its surrounding electrolyte and metallic contact is established between pin B and contact Tb. If very high working currents must be considered, it is advantageous to lower pin B into the electrolyte before metallic contact of pin A and contact Ta is broken; likewise, it is 0 advantageous to remove in such casepin A from its surrounding electrolyte only after metallic contact between pin 13 and contact Tb has been established.

If a construction is desired in whichseveral taps can be changed successively, the switching vessels and contact pins are arranged preferably in a row or juxtapcsitioned along the periphery of a circle, each two contact pins being connected to each other as shown in Figure 1. In practice, consideration must be given to the fact that the electrolytic fluid does evaporate because of the heat produced during the switching operation.

For this reason the electrolytic liquid is insulated at the top, as shown in Figure 2, by means of an oil layer. It is also advantageous to provide in such case a storage vessel'W which, however, need not necessarily be present in each and every vessel containing the electrolyte. It is for example possible to provide between the electrolytic vessels Ga, Gb, Gc, Gd thin insulating tubes Ra, Rb, Rc, Rd. Inasmuch as the voltage difference between adjacent taps is only small and, moreover, produces a varying electrolyzing current, the operation of the device is not impaired in any respect.

Instead of using an oil stratum disposed on top of the electrolytic fluid, it is also possible to use an insulating layer of heavy specific weight (e. g. tricresyl phosphate) which is disposed at the bottom of the vessel and serves as a closure against the air. However, it is always advisable to take care that the moving switch parts do not mix or emulsify the electrolytic and insulating liquids when moving from the one to the other.

For that reason, contact pins Cb, Cd of Figure 2 are constructed as tubes which are provided at their upper ends with pistons C having a diameter corresponding to the outer diameter of the contact tubes. When a contact tube is thrust from the insulating liquid into the electrolyte the amount of electrolyte displaced is drawn into the tube avoiding any disturbance in the strata of the liquids.

In Figures 3 and 4 a construction is shown in which taps 1, 2, etc., and lead-oil lines "A, B, etc.,

ias well ,as the electrolytic liquid are connected with each other by means of a conductive liquid such as for instance mercury. The mercury, as shown in Figures 3 and 4, is preferably disposed together with the electrolytic liquid: Y in an insulating tube into which the taps 1, 2 etc. and lead-oil contacts A, B, etc., project. In the constructions of Figures 3 and 4 the insulating tube has annular shape and consists of glass. 0

In the construction shown in Figure 4 the tube diameter is uniform. In the construction of Fi ure 3, on the other hand, the tube becomes narrower at contacts 1 and 2V in order to obtain, in operating position of the device, a greater distance between the lead-off contacts A, B and the idle tap contact 1. The tube is preferably disposed up-right and rotatable about a horizontal axis. In the position of the device shown in Figures 3 and 4, lead-oil contact B is connected to tap 2. II it is desired to change the contacts, for

asacae instance so as to establish contact between tap 1 and lead-0E A, this result may be obtained by turning the ring-shaped tubes L, M about a horizontal axis. Due to its weight the mercury and with it the electrolytic liquid Y will always remain in the lower part of the tube so that the desired change of contacts is obtained by simple rotation of the tube.

It will be apparent that the operation of the devices illustrated in Figures 3 and 4 as well as that of the device shown in Figure 2, is exactly the same as that of the construction of Figure 1 hereinbefore described in detail.

What I claim is:

1. In an electric current transformer comprising a plurality of taps for diiferent voltages, the combination of movable conducting means adapted to make contact with the said taps for taking oif current, and a variable resistance associated with each of said taps and adapted to oilfer to the current flowing to said conducting means, on approach to and withdrawal from each tap, a decreasing and increasing resistance, respectively.

2. In an electric current transformer comprising a plurality of taps oi difierent voltages, the combination of a plurality of movable electrodes adapted to make contact with the said taps for taking oiI current, and an'electrolyte surrounding said taps and oflering a variable resistance to the current flowing to the electrodes when the latter approach or withdraw from said taps.

3. In an electric current transformer comprising a plurality of taps of different voltages, the combination of a plurality of cells, contact pieces in said cells, said contact pieces being connected to the said taps, an electrolyte being disposed in :said cells and surrounding said contacts, and a plurality of interconnected movable contacts cooperating with the said contact pieces to switch over the current from one tap to another.

4. In an electric current transformer comprising a plurality of taps oi! diflerent voltages, the combination of a container, a plurality of cells in said container, contact pieces disposed in said cells and connected to said taps, an electrolyte being disposed in said container and surrounding the said contact pieces, an insulating liquid disposed on top of the electrolyte, a plurality of movable tubular contacts co-operating with said contact pieces to switch over the current from one tap to another. 5. In a device, as claimed in claim 4, a plurality of conduits between the said cells to establish communication therebetween, and an electrolyte storage vessel disposed in the container and communicating with the electrolyte containing cells.

6. A device, as claimed in claim 4, in which each of the said movable tubular contacts is provided at the upper end with a circular chamber having an inner diameter equal to the outer diameter of the tubular contact and a. piston moving in said circular chamber to draw up the amount of liquid displaced by the movable tubular contact.

BERNHARD JANSEN.

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