US1319720A - Protective device. - Google Patents

Description

D. T. MAY.

PROTECTIVE DEVICE.

APPucATmN msn |AN.18.|91B.

Patented Oct. 28, 19,19.

' than throuh UNITED STATES PATENT OFFICE.

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INCUEPOBATED, 0F NEW YORK, N.

Y., A CORPORATION 0F NEW YORK.`

PROTECTIVE DEVICE.

Specification ot Letters Patent.

Patented Oct. 28, 1919.

Application nlcd January Il, lill. lerill llo. 312,472.

To all whom t may concern:

Be it known that I, Davia T. MAY, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Protective Devices, of which the following is a full, clear, conoise, and exact description. p

This invention relates to protective devices for use in electric circuits exposed to 1i rhtning or like hazards, and is of the type which comprises a spark gap incloscd in a container from which practicallyI all the gas has been exhausted.

As is Well known, there is for each length of spark p a critical gas pressure at which the break own voltage, i. e., the voltage that will force a discharge across the gap rather the portion of the llne protected there is a minimum, and in practice the container is exhausted to about this pres sure.A If, through the cracking of the Walls of the container or from other causes, the pressure in the container increases beyond a certain point, the breakdown voltage is so much increased that the ga no longer affordsv a ath of discharge ior all voltages that Wou d be injurious to the apparatus to ,be protected. It has been proposed to provide protection devices of this type with automatic means for conductively bridging' the spark ga when. the pressure rises beyond the limit of safety, but although this maintains the protective function of the device it results in grounding the` line until the 4defective arrester is Igplaced by one whose spark gap is unbridg The device ,pf this invention includes two alternative spark gaps of different lengths and therefore having dill'erent critical pressures, in consequence of which one gap provides protection at the normal pressure in the container, and the other gap rovides protection when the pressure Aun uly increases beyond that for which the first gap is designed. A similar arran ment is coiI ered by the application filed y George H. Stevenson, Serial No. 132,446, filed November 20, 1916, for protective devices, assigned to the same assignee as the present application. This invention is an improvement thereon in that selective means are provided for interposing one or the other of said gaps in the path, which. must be followed by -n discharge through said device, theahther gap being at the same time removed from the dlscharge path. In-the accompanying drawing, Fi 1re 1 n*1s a cross-sectional view of one embo iment of my invention; F' a modified forgman Figs. 3.and Atare diagrams ofthe circuit arran ments of the devices shown in 1 an -2 respectively.

In a container 1 arcarranged electrodes 2, d and 6 of any suitable material. electrodes 2 and 4-is placed an insulat'm separator 1Q and between electrodes 4 'and 1s placed a second insulating sessarator 12 of greater tlukness than the parator l0.

here are thus formed two spark gaps of different lengths, the longer spark gap-fbotween theelectrodes4 and G-being usually of the length best suited to the `conditions under which the device is to be used.

In manufacturin tainer 1 is exhaustedg to the degree'of vacuum that will give the most eicient opepation of the longer spark ap, and while t degree cf vacuum exists t c discharge a includes this longer spark gap.` But i ou account 8l) of leakage or ionization of themctal of the electrodes or from other causes, the s preswhich he longer spark gap functions roperly, tl path d replaced by the shorter gap bctweon gie electrodes 2 and 4.

To e ect the substitution in the discharge path of one spark gap for the other, there 1s rovided a manometric valve or switch, 90

which in form shown by Fig. 1, is` 'constructed and operated as follows: A U-sha tube `14 is supported inthe container on t e stem 1 5. One end 16 of the tube is closed and the other end 18 is` open' and' covered b porous cap 20 which permits passais o air or other gas into and out of t e tube. Within the tube is the mercuryr column Brackets 24 and 26, of suitable conductive material, support the electrodes and are 10.0

conductively connccted'to electrodes 2 and 6 respectively; each bracket is secured to one oi' the legs of the U tube b a band 28 or the like. Each of the lea'ing-in conductors 30 and 32 forming the terminals 10,5

of the arrester and hermetically sealed into the stem 15 is connected to one end of ont` of the conducting brackets 24 and 26. To the other end of the bracket 24 is co d` the conductor 34 which passes thmugh the 2 is a similar view of 60 sure the container rises beyon` that at porous cap and extends into the interior of the manometer tube 14. To the other end of bracket 2G is connected the conductor 36, which extends into the interior of the munometer tuhc through its closed end 1G. From the electrode Al leads comluctor 38 which is hermciically Scaled into the wall of the hase of the [nanometer tube with its und extending into' the mercury column Q2. l

The parts are so proportioned and arm ranged that, with the pressure in the container that at which the longer spark gap between the elcctroifles 4f and G is adapted. to function satistactorilyQthe mercury columnQQ rests in the position shown in Fig.

1, that is, with the mercury enveloping,V the end of the conductor -l. The path et discharge then includes leadingn conductor 30, conductor bracket '34, conductor 34, niercury column 22, conductor 3H, electrode l, the longer spark gap, electrode 6, conduct ing bracket 26 and the leadingin conductor 3Q. This condition is diagrainmatically shown in Fig. 13 in which the conventional symbols denoting the various parts 'ot the circuit are indicated `by the same reference characters as are used in Fig. l.

If the pressure in the container rises, the

mercury column is'forced toward the closed end 16 of the tube until, when a verv tain pressure is reached, the contact between the 0nd 0f the mercury column and the conductor 34 is broken, and the opposite end of the mercury column surrounds and makes contact with the end of the conductor 36. The path of discharge then in-- cluclcs conductor 30, conductingr bracket 2l., electrode Q, shorter spark gap, electrode il, conductor 38, mercury column conductor 36, conducting bracket 2G and leading-in conductor 32.

The position of the ends of the conductors 3l and BG and the length of the mercurv column. is suoli that the contact lagnccn the conductor 3l and the mercury column is broken, and contact between conductor 36 and-,the mercury column is made whenever the pressure in the container becomes high enough to prevent the reliable functioning of the longer spark: gap. When the pressure is again reduced bly rexhausting the container, or otherwise, the mercury column returns to the position shown in Fig. 1 and the longer spark gap is restored .to the discharge path, Thus there results an automatic selective inclusion in the arrester discharge path of the sparlcgap funcL tioning most satisfactorily at the gas presi sure existing in the container.

In the arrangement shown in Figs. 1 and 3, the removing of eachspark gap from l. the discharge path is secured 'by short-circuitiug the gap. In the modified. arrangement shown .in Figs. 2 and 1, thememoving of the spark gap is secured by cutting it entirely out of the circuit. fied arrangement, the leading-in conductor 40 is sealed into the wall of the base of manometer tube 14 with its end extending into the mercury column 22. and the leading-in conifluctor 42 is connected to the mid.- dle electrode el. The electrodes 2 and 6 are connected through. the conductive brackets 24 and 26 respectively to the conductors 44 and lo'. Conductor 44 passes through the closial end 16 ot' the manometer tube 14 and the conductor -16 is lcd through the porous cap 2() into the open end 18 of the manometc-r tube.

With the pressure in the container 1 that In the modiat which the longer gap functions satisfaciorily, the mercury `column is in the position shown in Fig. 2 and the discharge path includes leading-in conductor 40, mercury column comluctor 4G, conductor brackets :26, electrode n, the longer spark gap, electrode 4. and leadingin conductor 4Q. lVhen the pressure exceeds that at Whih the longer nap can he relied upon, the mercury colmar. is moved toward the closed end l5 of the teilw, breaking contact with conductor .lll and making" contact with the conductor Ylfl. The discharge path is then through lending-in conductor 4U, mercury column 2;), conductor 441-, conductor bracket 24, elecn trode :2. shorter spark gap, electrode 4. and lcadingrin conductor 42.

It is apparent that if the conditions 'of an installation should make such a course desirable, either of the above forms of my in vcntion could he arranged with the shorter spark gap normally in the discharge path, :L change in pressure resulting in the substitution of the longer gap therefor.

lVhat is claimed is:

l. ln a. protective device arranged to afford a discharge path for electrical charges and comprising,1 two spark gaps, selective snltuhing means for including one or the other o' said spark gaps in said discharge path.

El. ln a protective device arranged. to a'ord a discharge path for electrical charges and comprisinp,l two spark gaps of different lengths, selective switching' means for incli'n'ling one or the other of Said spark gaps4 dnetor's to the electrodes at the opposite ends (,f one or the other of` saill si'iarl gaps.

5. In a protective device, a container` a pair of conductors entering, said container and forming the terminals ot' said device, electrodes in said container providing spark gaps of diil'crent lengths, and nicans'controllcd by the IJas pressure in the container for selectively connecting Vsaid conduct-ors to the electrodes at the opposite ends ot' ont.I or the other ot' said spark gaps.

(i. In a protective devicera eontilincr, n pair ot' conductors entering said containciL and forming tile ternlinalscoff' sn'idY device, electrodes in said container providing spark gaps of different lengths, and a, inanonietrie switch in said container for connecting said condnctors to the opposite ends of one or the other of said spark gaps.

7. 1n a protective device, u container, a pair of cominctors entering said container and forming the terminals of said device, electrodes in said container providing spark gaps of di'erent lengths, and means for selectively connecting said conductors to opposite ends respectively of one or the other of said spark gaps, said means comprising a. Usliaped tube communicating at one end with the interior of Suid container and closed thereto at the other end, n. column of mercury in said tube, and contacts spaced along ling; said container and the interior of said tube and connected to the respective electrodes and conductors. y

S. In ai protect-ive device, a partially evite` aated container, electrodes therein roviding discharge gaps of different lengt s, said electrodes being sarronnded by gas at Substantially the critical pressure of the longer ga p, a pair of conductors forming the terminals of said device, the longer of said gaps being interposed `(between said conductors,

and means operating ln'wesponse to an increase of gas pressure in Suid container to substitute tli'e shorter gap Yfol' the longer gap.

79. In a protective device, s, partially evacuated container, a pair of conductors enterforining the terminals of said device, electrodes 1n said container providin, r a plurality of Spark gaps adapted to diiferent degrees of vacuum, sind conductors being connected to electrodes at opposite. ends of one of said spark' gaps, and switching means responsive to s. change of. gas pressure in the container for connecting said conductors toelectrodes at the '0p-5.-

posits ends of a dierent spark gap.

In witness whereof, I hereunto subscribe my name this 12th day of January, A. D., 1918.

DAVID T. MAY.

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