US2538177A - Excess-voltage arrester - Google Patents

Description

Patented Jan. 16, 1951 EXCESS -VOLTAGE ARRESTER.

Sten Daniel Vigren, Stockholm-,-W-alter Otto Wilhelm Broberg, Nynashamn,.and.- Ernst Martin Thiele'rs, Stockholm, Sweden, .assignors to, Telefonaktiebolaget L M Ericsson, Stockholm, Swe-- den, accompany of Sweden Application Septemberl; 1945, Serial No. 615,036 In Sweden April 3, 1944 Section 1, Public Law-69 ;August8, 1946 Patent expires ,April .3,-196 4n.

1 Claim.

The invention relates to a modification of excess-voltage arresters, especially with regard to such ones, as are usedin large quantities in low tension devices such as in telephone plants and in other low voltage devices. An excess-voltage arrester which is very common in telephone de vices is made of a spark gap withtwo electrodes, usually of =carbon,,said-electrodes being held at a short mutual distance, .for, instance by washers of insulating material, usuallymica. That type of excess-voltage arrester is described in the Swedish Patent No. 74,667, according to which electrodes and washers have received a suitable shape for the function of the arrester, electrodes and washers having furthermore been assembled into a single unit by means of insulating binding means.

Of late ,it has been proposed to use, instead of the described excess-voltage arrester, voltagedependent resistances (siliceous carbide, ocelit, etc.), which at normal operating voltages possess a hi'gh resistance, but underhigh voltages-show a very low resistance and thereby can dissipate the high-tension voltages.

Said arresters are mounted close to the part of the device whichis to be protected, and are connected between the branches of an aerial line and. earth. The latest, researchers have however proved, that inthunderstormsthe currentsin an aerial line (telephone line) can come up to 1500 amperes or still more. That fact places especially great demands on a good earth connection for the arresters. If the earth connection resistance comes up to 2 ohms, there will be, for said current, a tension of 3000 volts on the earth electrode, said tension being hardly'supportable by the insulation in a telephone apparatus or a telephone wire of norm-a1 construction. The earth connection resistance ought thus preferably to be below 2 ohms. However, such a low earth connection resistance cannot be obtained otherwise than at special places, at any rate not without exceedingly heavy costs. Even an earth connection resistance of ohms is difiicult to obtain.

The inventors have introduced a new way for connection of said excess voltage arresters, which differs from hitherto known ways, the arresters, instead of being connected between line branches and earth, are according to the invention connected between the branches and the metallic body of the apparatus, which supports the inner details of the apparatus. Said body may as a result of lightning obtain a high potential and the arresters are so provided, that the potential difhaving a great capacity to earth (water pipe,

central heating).

It is to be observed that with said arrangement the arresters will be less damasedby li htning than if they were directly connected to earth.

From another point of view-it is obviousthat it is not desirableto-touch thebody 0f theapparatus during thunderstormsit seems-to be of 4 minor importance, as the subscribers are ordered not, to use; the telephone during thunderstormsit is however to be observed, that the same voltage? conditions must arise, if at-break down occurs on the body, which during'lightning is a normal defectof said apparatus. The invention is moreover: intended fo telephone instruments with insulating casing, for instance; of -molded plasticgmaterial, which surround the body of the apparatus and the inner details it supports,,so that thebody is thusnot normally accessible from outside.

We think of the origin of atmospherical excesstension voltages, irrespective of direct downstrokes, more or less in the following way: In a static thunderfield, there arise charges on an aerial line (e. g. a telephone line with two branches). On changes of the thunderfield these charges are released and give birth to =a tension Wave on both sides along the telephone line. When said tension wave meets the parts of the device connected with the telephone line, break downs or flash-overs may take place on earthed part or on apparatus metallic details, which have great earthing capacities or not very good insulation against earth, respectively. The beforementioned way of connecting an excess-voltage arrester, for instance a carbon lightning arrester, between each of the branches and earth depends for its effectiveness on the supposition that the high-tension wave runs parallel to both branches, and that therefore no potential diiierence worth mentioning exists between the branches. In reality, however, the attenuation of the wave may often be different with regard to the two branches, and the charge of one of the branches may even for some reason be discharged in a larger or smaller degree.

With regard thereto the inventors have found another modification, wherein, besides said two arresters, there is also an arrester intended to be connected between the branches. Said latter arrester is then supposed to come into action should, for some reason, a potential diiference arise between the branches. Recent researchers have also proved that such a triple arrester obtains a higher protecting efficiency compared with previously known devices having only two protecting elements.

The described modifications will be more clearly illustrated by means of the figures in the accompanying drawing. Said figures refer more particularly to open spark gaps (carbon lightning arresters), but it is obvious that the principles of the invention may be applied with other forms of excessvoltage arresters.

Fig. 1 shows the connection in principle. Two sparkor discharge gaps G1 and G2 are connected in series to a telephone branch L1 and L2, and the point of contact between G1 and G2 is connected to the body A in a telephone apparatus. G3 is a spark gap connected right across the branches, which in turn are connected to usual selecting equipment LF.

Fig. 2 shows a unit made of three interconnected carbon lightning arresters K1, K2 and The line branches are indicated by L1 and L2 and the connection with the body of the telephone apparatus by B. The electrode blocks of the carbon lightning arresters are indicated at E and the insulating washers at M.

Fig. 3 shows a unit made of only four electrode blocks (E), out of which two (the central ones) have been provided with electrode surfaces on both their sides.

The embodiments may vary in still other ways. The assembling into one single unit may be effected in different manners, by means of screens, springs or, most conveniently, by means of insulating binding means.

The arresters thus described may, when they are to be combined with telephone devices, be placed in a suitable socket, eventually provided with a cover, close to the telephone apparatus. An additional conductor must then be carried from the apparatus case to said socket.

A new way, by which said conductor may be dispensed with, is to mount the arresters directly in the apparatus. Both ways may have their advantages, and the way of mounting may vary according to difierent circumstances and with regard to different practical considerations.

The invenventors have introduced one more novelty, i. e. that the unit, with regard to its outer shape, is so composed, that it cannot be installed otherwise than in the correct cdnnecting way. This is an advantage if the arrester is to be exchanged by a person unfamiliar with its construction.

We claim:

An excess voltage arrestor unit for equalizing the potentials in telephone apparatus components due to excessive voltages on line wires connected to said apparatus, comprising a plurality of more than two excess-voltage conducting layers, conductive electrode layers alternating with said excess-voltage conducting layers and supported in contact therewith to provide end and intermediate connection points for said unit, means for connecting intermediate electrode layers to respective wires of a telephone line, and means for connecting said end electrode layers by a common connection to a metallic portion supporting at least one of said components.

STEN DANIEL VIGREN. WALTER OTTO VVILHELM BROBERG. ERNST MARTIN THIELLERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 508,649 Thomson Nov. 14, 1893 1,303,383 Osborne May 13, 1919 1,573,068 Honaman Feb. 16, 1826 1,728,534 Fortescue Sept. 17, 1929 1,750,090 Stanton Mar. 18, 1930 1,799,174 Loye Apr."7, 1931 2,053,988 Ferris Sept. 8, 1936 FOREIGN PATENTS Number Country Date 147,270 Switzerland May 31, 1931 251,292 Great Britain Apr, 7, 1927

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