US2830216A - Multiple discharger particularly for protecting telecommunication nets and the method for manufacturing it - Google Patents

Description

Apnfi 8, 1958 s. LAUREN 28 m MULTIPLE DISCHARGER PARTICULARLY FOR PROTECTING T TELECOMMUNICATION NETS AND THE METHOD FOR MANUFACTURING IT Filed Sept. 24, 1954 United States Patent @fifice Patented Apr. 8, 1958 MULTIPLE DISCHARGER PARTICULARLY FQR PROTECTING 'IELECOMMUNICATION NETS AND THE METHQD FOR MANUFACTURING IT Silvio Laurin, Genoa, Italy, assignor, by nesne assignments, of one-half to Elsi lElettr-onica Sicula S. p. A., Palermo, Italy Application September 24, 1954, Serial No. 458,228

Claims priority, application Italy August 2:, 1954 6 Ciaims. (Cl. 3l3188) It is well known thatin various systems, particularly in telecommunication circuits, protection against voltage surges of external origin is realized by the use of discharge devices assuring an available insulation between the electrodes as long as a voltage value producing a discharge in ionized gas with the passing of current to ground is not reached.

It is the object of the present invention to provide a multiple discharge in rarified gas particularly for protecting telecommunication circuits, and the like, such as to be able to withstand strong discharges of the current to the ground.

In general, the object of the invention is also a method for manufacturing the said discharger.

The discharger according to this invention is characterised by the presence of a plurality of electrodes assembled in the same bulb that contains a rarefied gas, in this manner obtaining the result that, even if the discharge begins between twoelectrodes only, it will further cause the ionisation of the gas and therefore puts all the electrodes in a conductive atmosphere, so that the residual voltages among them are maintained Within limited values, one of the electrodes being connected with the ground.

The discharger according to the invention is thus characterised in that the grounding-electrode and the other line-electrodes enclosed in the bulb are constituted of substantially parallel plate elements and that in order to help the propagation of ionization, the central electrode constituting the grounding-electrode is provided with small holes or is formed by a grate or a net.

The discharger according to the invention is further characterised in that in order to allow a direct discharge between the two line wires at given surges of voltage, the corresponding line-electrodes enclosed in the bulb present a more closely spaced zone on their surface corresponding to the gap for the usual flashing-over or arcing voltage.

The discharger, according to the invention, in case of presenting a substantial plurality of line-electrodes in the inside of the bulb, is characterised in that the groundingelectrode is constituted by a plate, while each one of the line-electrodes is constituted by a cylinder perpendicular with respect to the surface of the plate.

In this last case, the discharger is characterised in that in order to help the flashing-over of the discharge, the plate constituting the grounding-electrode presents in its center a protuberance that reduces the distance to the line-electrodes.

Before further indicating characteristics of the discharger according to this invention it is convenient to recall the fundamental characteristics of the method for manufacturing the discharger, particularly of its electrodes.

The method, according to the invention, for manufacturing the electrodes for the discharger, is characterised in that the electrodes activated and suitable for discharging in rarefied gas, are obtainedby forming salts of alkaline-earth or alkaline metals on abearing metal having amphoteric reaction and high fusing point-and subsequently heating under vacuum the electrodes coated by said salt till a coating of oxides of alkaline-earth or alkaline metals will be formed, which, notwithstanding, contains the said salts as a binding of said oxides with the bearing metal, in which latter these salts are partially melted or dissolved.

In a preferred embodiment the method is further characterised in that the bearing metal is molybdenum, tungsten or any other metal having similar characteristics.

The method according to the invention for manufacturing the activated electrodes for discharges suitable for discharging in rarefied gas is particularly characterised in that on a bearing metal having amphoteric reaction, a hydrate of an alkaline-earth or alkaline metal is deposited, and subsequently the bearing metal thus coated will be heated, under the vacuum, above 1000 C. till a super ficial coating of oxides of alkaline-earth or alkaline metals is formed, adherent to the base metal by means of a binding made of amphoteric salts of the said metals and the bearing metal.

The said method is further characterised in that in place of the hydroxide of an alkaline-earth or alkaline metal, a mixture of hydroxide, oxide and carbonate of said metal or metals is used, with the hydroxide predominating in the composition of the mixture.

In one of its embodiments, the method is characterised in that in place of the compound of alkaline-earth metal, a mixture of the corresponding compounds of each one of the three alkaline-earth metals: barium, strontium, and calcium, is used.

The method is particularly characterised in that the bearing metal is constituted of molybdenum reduced into a very thin plate.

The method is finally characterised in that the bearing metal is previously treated for instance by sanding and/ or oxidation or the like, in order to get a better penetration, adhesion and chemical combination of the activated coating with the base-metal.

The discharger according to this invention is particularly characterised in that its electrodes are constituted by thin plates of heat resistant metal, preferably an amphoteric metal such as molybdenum, tungsten, tantalum and the like, activated by means of the said method.

The discharger is further characterised in that the electrodes are disposed so that the discharge currents either to the ground, or among the electrodes themselves form windings, the magnetic field of which has the tendency to localize the discharge at the ends of the electrodes themselves.

In a preferred constructive embodiment, the discharger is characterised in that the electrodes are disposed with their axes parallel one another, the currents being led to the electrodes at the end opposed to the one where the discharge is wanted to be localised.

The discharger is still further characterised in that the electrodes are disposed so as to realise the least distance between the ends opposed to those ones to which the currents are led, all the currents being led to theelectrodes at the same end of the tube.

In a preferred embodiment the discharger is characterised in that the bulb presents a radioactive material suitable for maintaining a substantial ionization in the gas contained in the tube, owing to the effect of the radiations emitted by the said radio-active matter, thus stabilizing the flashing-over voltage for discharge in the darkness.

The said discharger, in one embodiment, is characterised in that the radio-active matter is deposited on one or several electrodes.

Finally, the said discharger, in another embodiment,

is characterised in that the radio-active matter is applied on the glass of the tube and adhered to it by means of a solvent, or it is fused (or dissolved) in the glass itself.

In the accompanyingdrawing some preferred embodiments of the object of the invention are shown only by way of example. Figs. 1, 2 and 3 are three diagrammatic views of a multiple discharger for a two-wire line; the Figures 4, 5 and 6 are three diagrammatic views of a multiple discharger for a four-wireline.Fig. 7 is a diagram for the connection of a multiple discharger in a two-wire circuit and Fig. 8 is a diagram for the connection of a multiple discharger in a four-wire circuit. Fig. 9 is a diagrammaticview of a five-electrode discharger; Figures 10 and 11 show the positioning of the electrodes for two particular cases. Figs. 12 to 15 show various dispositions and formations of the electrodes; Fig. 16 shows a particular embodiment of the diseharger.

The discharger for a two-line circuit shown in the Figs. 1, 2 and 3 comprises a glass-bulb A filled with a convenient rarefied gas (for instance argon or any other rare gas) in which, in the center the grounding-electrode B, and parallel thereto, on either side of it the two lineelectrodes C and D are disposed. The electrodes are respectively connected with the ground and with the linewires through the conductors b, c, d projecting from the bulb.

In order to better the rapid propagation of the ionization in the zone of that electrode coming second in the discharge, the grounding-electrode B is provided with small holes; further, in order to make possible a discharge between the two wires for particular surges of voltage, the two line-electrodes C and D have a given portion of their surface at approximately the flashing-over distance previously determined for the usual flashing-over voltage, as illustrated in Fig. 3.

In another embodiment, not shown in the drawing, the ground-electrode B may be constituted by a grate or by a net, inplace of the bored plate, without any change of the other characteristics of the discharger.

The'discharger for a four-wire line is analogously constitutedas*illustrated in'Figs. 4-, 5 and 6by a glass bulb E, containing rarefied gas, a grounding-electrode F having the shape of a plate, four line-electrodes G, H, I, L having cylindrical shape andthe conductors g, h, i, l for connecting the corresponding electrodes with the outside.

The cylindrical plate F constituting the groundingelectrode has at its center a protuberance designed to locally diminish the distance between the line-electrodes and "the grounding-electrode, in order to intensify the local electricfield and therefore help the flashing-over or arcing of'thcdischarge.

The central positioning of the said protuberance has further the obiect to cause the fiashing-over (or arcing) of the first discharge to occur in a zone as near as possible to the other electrodes, in order to facilitate the successive flashing-over (or arcing) of the discharge in these electrodes.

The manner of positioning, according to the invention, a multiple discharger in a two-wire circuit is shown in the Fig. 7. 1 and 2 are overhead wires of the line, 3 and 4 are the fuses against surges of current, 5 is the load device, and 6 is the multiple discharger according to the invention, shunt connected between'points 7 and 8 ahead of the fuses and grounded at T. I

The positioning of a multiple discharger, according to the invention, is similarto that of Fig. 7 when inserted in the four-wire circuit shown in Fig. 8. The wires 9, it), 11 and 12 of the line go to the translators 13 and 14, through the corresponding fuses 15,16, 17 and 18.

The multiple disc-harger is shunt-connected between points 24), 21, 22 and 23 ahead of the fuses and is grounded at T.

Referringto Fig. 9 there-is shown a diagrammatic view of a discharger with five electrodes. The eentralelectrode .irthasa eylindrical:surface and a terminal 25 that is cond nected with the ground. The other electrodes 26, 27, 28 and 29 are symmetrically disposed with respect to the central electrode 24 and have terminals 3%), 31, 32 and 33 and discharge towards said central electrode.

The positioning of the electrodes with parallel axes, having all the current leads at one end, as it may be seen in Fig. 9, causes the discharge to be located at their opposite ends owing to the known rule that a winding traversed by a current has the tendency to take such a shape as to comprise the highest flow. The zones in which the discharges are located are shown at 341 in Fig. 9. The concentration of the discharges has the advantage that the lower zone is not working; therefore the best maintenance of the activating surface (obtained by means of a method that will later on be described) will be assured; further the Zone of highest heating is far from the terminal weldings and from the entry of the leads through the glass, which constitute the vulnerable points for the surges of temperature.

The construction of the electrode which (as will be described below) is made of a thin plate, having a large surface, assures for a substantial cooling of the discharging lower zone, thus preventing the temperature at the points at which these plate elements are welded on the leads, from reaching 700 C., even with the highest charges.

Finally by the said construction, a light electrode is obtained, having a large surface and therefore little thermal inertia. This allows a rapid heating of the electrodes themselves and therefore the passing between the electrodes of low voltage discharge; this is very useful for operating purposes in order to drain to the ground voltage surges with high currents substantial duration.

Referring to the Figures 10 and ll, that for the sake of simplicity show dischargers having only three electrodes. Fig. 10 shows the device having parallel electrodes in which the discharge, beginning to respect any one of two points of the two nearest longitudinal lines, indicated in 35, 36 or alternatively '37, 38, is successively displacing towards the ends indicated at 34, owing to the magnetic field produced by the currents, the direction of which is indicated by the arrows 39.

Referring to Fig. 11 it is seen that the electrodes are convergent in order that there may be the least distance in the zone indicated at 34, at which the discharge will establish itself; the flashing-over (or arcing) discharge itself will preferably happen at the less distant points comprised in'this zone.

in whatever type of the aforesaid dischargers it will be convenient to add some radio-active material, that is preferably deposited either on the grounding electrode 24, only and particularly on the end that is opposite the upper edges of the other electrodes or, as shown in Fig. 9, at 40 on the bulb.

Figs. 13 and 14 show various constructions and arrangements of the several electrodes. This Fig. 12 shows that the electrode 24 which is to be grounded has the shape of a hollow cylinder in the inside of which the other electrodes 26 and 29 areplaced. In this figure it is further shown by dot and dash lines on the electrode 27 that the electrodes may have the shape of a tip 41 directed towards the peripheral upper edge 42 of the groundingelectrode 24.

Fig. l3'shows that'the grounding-electrode 24 may have the upper end mushroom shaped, whilst the electrodes 26 and 28 have their upper ends terminating in curved tongues 44-so that their shape corresponds to the shape of the outer surface 43 of theelectrode 24 and further so head of electrode 2d, thus realizing the collecting of all discharges in the zones 34.

"Fig. 14'shows the-grounding-electrode 24 ashaving the shapeof a glass flared at 47 and electrodes '26 and 28 present intheir upper portion acurved tongue 48 directed 5 so that its edge 49 will be in front of edge 47 of electrode 24, providing the least distance between the electrodes 26 and 28 and the electrode 24. The discharges will therefore substantially be limited to the zones 84.

Fig. 15 shows the grounding-electrode 24 as having the shape of a bell or a plate above the upper ends of the electrodes 26 and 29 which are curved so that their upper ends 49 are positioned at the least distance with respect to the edge of electrode 24; with the purpose of locating or collecting the discharges in the zones indicated by number 34.

Finally, Fig. 16 shows that the grounding electrode 24 has the shape of a bell enclosing the electrodes 26 and 2%, so that the electrode 24 has also the function of a bulb for the discharger.

A further object of this invention is to provide a particular method for manufacturing these electrodes.

Ionically heated cathodes are known with thermionic emission; but for high currents these are constructed with a structure having a high thermal inertia, so that it is impossible to use them for devices functioning by discharge, which have further the requirement of insulation as soon as the current ceases. Further, the electrodes of the dischargers often undergo discharges having a voltage of the order of l-200 volts between the electrodes; in these conditions, the known electrodes activated with oxides of alkaline-earth metals are soon no longer active, owing to the wearing out of the coating of oxide. The constructions heretofore adapted for the electrodes of dischargers consist in the use of pure metals such as those belonging to the group aluminum, or zinc, that easily emit electrons under ionic bombardment, but which have the inconvenience of a low fusing point and are consequently not capable of withstanding very intense surges of charge; or the use of heat resistant metals as tungsten and molybdenum but for which the discharge is not so easily achieved and occurs only with higher voltage drop in the arc, with consequent fusing in case of heavy charges. Both these constructions do not allow a large current field in which the working of the discharger may be active.

Generally, the use of heat resistant metals gives a less available flashing-over and demands for the electrodes a shape having tips on which the fusing of the metal of the electrode happens in the case of a surge.

In order to obviate these inconveniences, a kind of electrode has been produced, which is the object of this invention, constructed with heat resistant material, but activated by means of a special method.

Molybdenum has been chosen as easier in use, but also tungsten, tantalum, and zirconium and the similar metals can be used. It is important to make the electrode from a thin plate and that it be shaped so that the arc will occur at one end and/ or it may displace towards one end and the magnetic field. Due to the discharge current will contribute for fixing the arc in said position. In case of high currents, this causes a heavy heating of the electrode in a determined zone which is extended as the current increases with the result that it assures a sufiicient surface having high thermionic emission.

The use of a thin plate for the construction of the electrode allows the gradual passing of the discharge with cold electrodes, characterised by an arc voltage of 200- 3G() volts and with a discharge with incandescent electrodes characterised by a voltage of about 5l5 volts.

The efficiency of the emission is assured by the activation with the result that the reaching of fusing temperature is prevented, as, by increasing the electronic emission, the dropping of voltage among the electrodes is diminished and consequently also the heat produced. The activation is made by means of alkaline earth metals, but by means of a method that is different from the well known one, using salts of said metals coated by means of a binder on the base metal and successively transformed to oxides by means of heating under vacuum.

The activating material is substantially composed of hydroxides of alkaline-earth metals in aqueous solution. The solution may be saturated in order to have in suspension, as an impalpable powder, the hydroxides, the oxides and salts of metals of the alkaline-earth group. A mixture particularly suitable to constitute an activating coating on the base metal and resistant to ionic bombardment, is constituted by: 50% barium-hydroxide, 25% barium-oxide, 25% barium-carbonate. A plurality of metals of the group barium, strontium, calcium and similar equivalents may be comprised in the mixture; it may notwithstanding be conceived to substitute for each aforementioned compound of barium a mixture of the corresponding compounds of alkaline-earth metals.

Special care must be taken in preparing the surface of the base metal.

The method followed in the described manner of manufacturing consists in sanding the surface in order to get a rough upper surface on which there will be a substantial adherence of the activating material.

Superficial oxidation of the base metal constitutes also an advisable preliminary treatment.

The activating coating deposited through immersion of the treated electrode (sanded, oxidated or the like) is allowed to dry owing to natural evaporation of the water. It is to be remarked that hydroxide, owing to carbon-dioxide contained in the air, has the tendency to form a carbonate and therefore the coated electrodes must not remain too long in the air, before being enclosed in their own bulb and under vacuum. During the evacuating of the tubes, the electrodes are heated up to a temperature below 300 C., the hydroxide fuses and forms a kind of very tough enamel in part combining with the base metal; heating is further increased till the forming of an oxide adhering as a very thin and tough film on the metal. The electrode thus constructed resists the strong ionic bombardment there is during the functioning, the activating coating not being swept away.

Further the flashing-over tension of the cold discharge is not submitted to substantial variations during the life of the tube owing to the yield of the activating coating.

Referring to the construction of electrodes activated by means of hydroxides it is important to remark that the proposed base metals molybdenum, tungsten, tantalum are amphoteric, that is that they are in condition to form some acids of which the saltsof alkaline and alkalineearth metals are known; these salts, when heated, show some solubility together with the bearing metal they come from; this explains the high adhesion and stability of the activating coating on the electrode. Forming of these salts helped by the presence of hydroxides of the alkalineearth r'netals, whilst oxides forming the carbonates of the same metals seem not to react with the amphoteric base metal and scarcely adhere on it.

An electrode obtained by this method has suficient capacity to emit electrons even in cold condition, thus assuring a discharge also at very low currents. In order to improve the characteristic of flashing-over of the discharge, particularly when the discharge is in the dark, some radioactive materials are added, so that in the gas enclosed into the bulb there will be some ionization even before forming the discharge. For this purpose cobalt 60 salts are used, particularly chloride or nitrate, in a diulted solution of the corresponding acids. A drop of nitrate of cobalt solution is placed on the central electrode (the grounding-electrode). During the evacuation, the nitrate decomposes, leaving a small coating of oxide of cobalt 60 on the electrode itself: the radiations emitted by the radioactive metal are sufficient to assure the desired starting ionization in order to establish an instantaneous flashingover voltage inthe light as well as in the darkness.

Another method consists in placing the cobalt salt on the glass of the bulb and fixing it on same by means of a fusing such as boric anhydrate; heating the cobalt 60 at 400 C. it will be fixed on the glass. At a temperature 7 of about 500 C. the oxide of cobalt dissolves on the glass and no fusing matter is necessary.

Though this invention has been described with reference to the embodiments shown in the annexed drawing, many practical improvements may be made in the embodiment of the idea, all based on the fundamental spirit of the invention itself as defined in the following claims.

What i claim is:

1. A protective device particularly for protecting telecommunication electrical circuits of the type which utilize electrical discharges through gases in an enclosed envelope, comprising a plurality of thin section electrodes, said electrodes including a cylindrical center electrode, and line electrode having arcuate cylindrical surfaces, and being arranged around the center electrode with vertically parallel axes, said electrodes being so disposed that convex surfaces affront each other, said electrodes having connection with the circuits to be protected and ground at the same end of the envelope, whereby a localized and concentrated discharge area is obtained reducing the ionization and de-ionization times with rapidly varying voltages and currents.

2. A protective device particularly for protecting telecommunication electrical circuits of the type which utilize electrical discharges through gases in an enclosed envelope, comprising a plurality of thin section electrodes, said electrodes including a cylindrical center electrode having perforations to assist in the propagation of the ionization, and line electrodes having arcuate cylindrical surfaces, and beingarranged around the center electrode with vertically parallel axes, said electrodes being so disposed that convex surfaces alfront each other, said electrodes having connection with the circuits to be protected and ground at the same end of the envelope, whereby a localized and concentrated discharge area is obtained reducing the ionization and de-ionization times with rapidly varying voltages and currents.

3. A protective device particularly for protecting telecommunication electrical circuits of the type which utilize electrical discharges through gases in an enclosed envelope, comprising a plurality of thin section electrodes, said electrodes including a cylindrical center electrode, and line electrode having arcuate cylindrical surfaces, and being arranged around the center electrode with vertically parallel axes, said electrodes being so disposed that convex surfaces affront each other, said electrodes having connection with the circuits to be protected and ground at the same end of the envelope, resulting in a cool zone in the lower part of said envelope to reduce thermal shock and cycling in said envelope.

4. A protective device particularly for protecting telecommunication electrical circuits of the type which utilize electrical discharges through gases in an enclosed envelope, comprising a plurality of thin section electrodes, said electrodes including a cylindrical center electrode, and line electrodes having arcuate cylindrical surfaces, and being arranged around the center electrode with vertically parallel axes, said electrodes being so disposed that convex surfaces affront each other, said electrodes having connection with the circuits to be protected and ground at the same end of the envelope, said envelope being coated with an electron emitting material, said coating cooperating with said manner of connection and said arrangement of axes and surfaces to reduce the minimum breakdown voltage and assist discharge in darkness.

5. A protective device particularly for protecting telecommunication electrical circuits of the type which utilize electricaldischarges through gases in enclosed envelope, comprising a plurality of thinsection electrodes,

said electrodes including a cylindrical center electrode,

and line electrodes having arcuate cylindrical surfaces, and being arranged around the center electrode with vertically parallel axes, said electrodes being so disposed that convex surfaces alfront each other, said electrodes having connection with the circuits to be protected and ground at the same end of the envelope, said center electrode being made of a metal capable of amphoteric reaction preferably molybdenum and coated with an electron emitting material comprising cobalt nitrate, said coating cooperating with said manner of connection and said arrangement of axes and surfaces to reduce the minimum breakdown voltage and assist discharge at low voltages in darkness.

6. A protective device in accordance With claim 1, with means of reducing the loss by ionic bombardment of electron emitting material whereby the center electrode is made of a metal with a high fusing point and is capable of amphoteric reaction preferably molybdenum, and is coated with salts of a member of the group consisting of alkaline earth metals and alkali metals, said salts and said electrode being heated successively under vacuum until oxides of said salts form a binding compound.

References Cited in the file of this patent UNITED STATES PATENTS 1,649,035 McCoy Nov. 15, 1927 1,680,518 Holden Aug. 14, 1928 1,941,956 Seibt Jan. 2, 1934 2,039,637 Dimond May 5, 1936 2,589,697 Hullegard Mar. 18, 1952

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