US1144029A - Protective device. - Google Patents

Description

E. E. F. CREIGHTON.

PROTECTIVE DEVICE.

APPLICATION FILED JAN. 5, 1914.

Patented June 22, 1915.

a? It Witnesses: lhventor Y Elmer -E.F.Cre i 2hton His Att orneg.

STAT S PATENT OFFICE.

sauna E. r. canmn'romor scnnnnc'rnnr, NEW roan, assreuon 'ro GENERAL unnernrc couramr, a conronarron or NEW Yonx.

PROTECTIVE DEVICE.

Original application !iled larch 19, 1913,

To all whom it may concern:

Be it known that I, ELMER E. F. CREIGIP' I TON, a citizen of the United States residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Protective Devices, of which'the following is a specification.

This application is a division of my application filed March 19, 19 13, Serial'No. 55,529, and relates to devices for protecting circuits from abnormal voltages, lightning ,and' similar disturbances, and more especially to protective devices for 'cll'CllltS of low normal operating voltage.

The protective device most-commonly used for telephone circuits, signal circuits and similar systems of low normal operating voltages and transient disturbances without dangerous delay and before the abnormal. voltage rises to dangerous value.

voltage, is a form of spark gap lightning arrester comprising essentially two electrodes separated by' a very short air gap. The air gap has an appreciable time lag, as it will not break down the very instant an excess voltage appears, and is furthermore liable to be bridged by dust, dirt and by the metal carried from the electrodes by a heavy dischargei Theobject of my invention is to provide a protective device which does not have the defects of the usual spark gap lightning arrester and which will remove abnormal My invention comprises-certain novel features set forth more particularly in the appended claims,- but the invention itself will i be better understood in connection with the longitudinal section of a form of arrester in which the discharge takes place in a horn gap mounted in the vacuum chamber.-

arranged Serial No. 755,529. Divided and this application filed January 5, 1914. Serial No. 810,275.

i In the particular form of arrester shown in Fig. 1, the tube 18 contains electrodes 19 mounted eccentrically to a ground ring-20 operating surfaces-j of the electrodes, in

which gap it is automatically lengthened and ultimately extinguished. The electrodes 19 and the ground ring 20 are carried in a yoke 21 made of porcelain or other suitable insulating material and fitting the.

tube 18 so as to held the parts in proper relation. Stoppers 2 2 are mounted adjacent the yoke 21 and are made of some suitable porcelain like material which can be baked in the tube and which will not giveolf gases when heated. The stoppers 22 are backed up by layers 23, 24 and 25 of different kinds of waxes which form air-tight joints with the tube 18 and also with the leading-in wires 26, which are connected at their inner ends to the electrodes 19 and at their outer ends to connection plates 27 embedded in the porcelain end blocks 28. r

The protective device constructed as above described is exhausted to produce in the metal tube a partial vacuum of such a value that lightning and similar abnormal disturbances 'are removed from the line with miniv mum delay and resistance. The desired vacuum may easilybe obtained by pumps,

such as are commonly used in the' art, and after the tube is exhausted it may be hermetically sealed in any suitable way. In

many cases I prefer to first fill the tube with some suitable gas and then exhaust it to. the required vacuum, so as to leave in the tube a residual atmosphere of that gas. I prefer v to use as a residual gas some of the monatomic gases, such as argon, neon, helium, or hydrogen, especially theinert atmospherlc gases, such as argon or neon, although a re- Sidual atmosphere of air or nitrogen will give satisfactory results. The proper pressure of, the residual as depends upon the nature of the gas int c tube and upon the size ofthe ap. I prefer to use a pressure such that idle equivalent needle gap is a muchenergy. By heating up the electrodes the brush discharge may actually hinder the formation of the spark discharge and the This preferred pressure is above the ,critical relief of the system, especially where the arrester is used on comparatively low volt age direct current systems. I so space the electrodes that at the preferred pressure, the

spark discharge occurs almost simultaneously with the appearance of a brush discharge and at a voltage somewhat above the normal voltage of the system to be protected.

pressure at which the spark potential is a minimum. A

A lightning arrester should permit 'the passage of transient over-voltage and very I high frequency oscillations with a minimum time lag. By high frequency, I mean oscillations and oscillatory dischargesofthe frequency of lightning or of the spark discharge of condenser, probably from one-half million to several million cycles per second. The time lag must beso small that the transient over-voltage will not have time to puncture the insulation. The spark discharge should occur without appreciable time lag in response to the application of a transient high voltage of minimum amount over the normal potential of the system. I

reduce the time. lag to an unobjectionable amount by, adjusting the gas pressure and the spark. gap without seriously affecting the minimum equivalent needle gap. I have found that at pressures above 10 mm. of mercury, the time lag is not enough to be .i objectionable, but that it is serious at lower I pressures, increasing veryflrapidly as. the

pressure decreases.

I, therefore, make the pressure such and so space the electrodes that the time lag is unobjectionable, the equivalent needle gap is at or near the minimum, and spark potential is reasonably low.

Under some conditions Iaccentuat'e the arc extinguishing feature of the circular horn gap formed between the eccentrically disposed electrodes 19 and the ground ring 20 by so proportioning the space around the -electrodes that upon a severe and long con tinued discharge the residual gases in the arrester expand to such an extent that their pressure is very greatly increased and their are extinguishing effect is correspondingly increased. The are extinguishing efle'ot of the arrestersishown'in the other figuresof the drawing maybe increased thesame way if consldered advisable, although I pres fer to so proportion the arrester that the pressure of the residual gases is increased a but slightly during the usual discharge,

Discharges through the protective device may be very severe and long continued,'if

the telephone or signal circuit is crossed with; e I

a lighting or ower, circuit having a potential considera ly higher than the potential at which the protective device discharges; vUnder these conditions the system should be grounded to protect the apparatus connected to it. In addition the continuous and heavy I discharges heat the electrodes and the adj acent portions of the arrester so hot that sufliv y cient gases are evolved to lower the vacuum, I and ingeneral the arrester is'deteriorated to e such an extent that it should be removed and replaced by a new 'one.,' In order to. an tomatically ground the system when crossed with a higher potential system, and to facilitate detection and removal of the arresters which have been injured, I provide means whereby the electrodes are automatically bridged and short circuited and are also connected to ground when the electrodes areheated to a certain extent. The preferred means for securing this result, as applied to the particular form of arrester shown in.

Fig. 1, comprises fusible metal films 29 secured to. the faces of the electrodes 19 and made in the form of disks of less diameter than the electrodes. The are or discharge from the edge of the electrode '19 does not touch the fusible disk,-which is heated only by conduction of heat from the electrode. As the, disks 29 are in intimate contact with the electrodes 19 a rise in temperature of the electrodes will cause the disks 29 to melt and the molten metal will run down and form a conducting bridge between both el'eetrodes and theground electrode, which in this case is the ground ring 20. When thls has occurred, the short circuited arrester may easily be detected by suitable tests and I then replaced.

In some forms of arresters designed to i withstand severe and continued discharges,- it is desirable to protect as far as POSSlblB.

the waxes and other material of the, seal from undue heating by the action of the are between the electrodes. I attain this result by placing the electrodes at a considerable distance from the seal and connecting them to the leading-in wires through metallic. connections 'so proportioned as to have a a radiating surface bywhichheat if:

transmitted from the hot electrode will be.

radiated to the tube and the surrounding nll very great atmosphere, instead. of being transmitted diy rectly to the leading-in wire and thenceto the seal. If desired, theradiation of heat may be increased by imme'rsingthe tube in a liquid or similar cooling medium.

. A modification in which the extinguishing action of the horn gaps is secured, is shown .in Fig. 3. a An evacuated glass bulb 42 contains a ground electrode 43 which coiiper- 5 ates with two line electrodes 44 so positioned with relation to the ground electrode 43 A as to form therewith horn gaps inwhich the arc may rise vertically and be extinguished. To prevent the possibility of arcs following the electrodes 44 down to the seal and thereby injuring the seal, I coat both of the electrodes near the seal with a protective coating 45 of refractory insulating'material so 1 that the arc cannot reach the electrodes at In this form of arrester the electrodes are sealed into the glam stem ofthe vessel 42, but the seal between the electrodes and the stem is not relied upon to hold the vacuum. The seal is made tight by fi]ling thestem with suitable wax 46.

' My invention may be embodied in many other ways thanthbse described and I, therefore, do not limit my invention to the precise arrangements disclosed except in so far as ii is limited by the scope of the appended .c aims.

. What'I claim as new and desire to secure by Letters Patent of the United States, is,--

1. A protective device comprising an evacuated vessel containing parallel disk elcctrodeshaving a common axis, and a grounded ring surrounding said electrodes and spaced away from the edges thereof, the axls of said ring being eccentric to the axis of said electrode.

2. A protective device comprising an evacuated vessel and electrodes in said vessel spaced away from one another to form a spark gap which increases in width in the direction of movement of thearc in said gap whereby the are is lengthened and broken.

3. A protective device comprising an" evacuated vessel, electrodes in said vessel pointscloseenough to the seal to injure it."

having curved codperating surfaces spaced about an axis eccentric to the axis of the other electrodes and spaced away from the edgesof said other electrodes to form'spark gaps to ground.

5. A protective device comprising disk electrodes mounted face to face, each of said electrodes having on its face-a disk of fusible metal smaller than said electrode, and

a grounded electrode spacedaway from the lower edges of said other electrodes to form spark gaps which are bridged by the melt ing of said fusible metal.

6. A protective device comprising two electrodes mounted in thermal relation to a body'of fusible metal, and a third electrode mounted beneath the other electrodes and spaced away from them to form spark'gaps which are bridged by said fusible metal.

when it is melted by a rise intemperature of said electrodes. o j

' 7. A protective devlce comprising an evacuated vessel, a disk electrode in said vessel, a cooperating annular electrode mounted eccentric to said disk electrode and separated therefrom to' form a spark gap between the edge of said disk and said an nular electrode.

In witness whereof, I have hereunto set my hand this 3rd day of January, 1914.

ELMER E. F. CREIGHTON.

witligesses: B H

ENJAMIN ULL, HELEN Onronn.

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