US1269534A - Protective device. - Google Patents

Description

G. F. GRAY.

PROTECTIVE DEVICE.

APPLlcATloN FILED FEB.3.1916.

Patented June 11, 1918.

Fig. Z.

Inventor Geor" e F' Gr'fag, b5 QM;

H IS fittorneg y UNITED sTATEs PATENT oEErcE.

GEORGE FRANCIS GRAY, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTIVE DEVICE.

Specication of Letters Patent. Patented June 11, 1918.

Application led February 3, 1916. Serial No. 76,049.

To all whom it may concern.'

Be it known that I, GEORGE F. GRAY, 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.

My invention relates to protective devices for systems of electrical distribution and more particularly to that class of protective devices known as lightning arresters.

The object of my invention is to generally improve protectivedevices of this type and particularly to provide a novel and improved lightning arrester of the vacuum ty e.

It is known that, with arresters in which the spark gap between electrodes is located in a vacuum, when the critical voltage is impressed across the electrodes of such an arrester, the spark gap does not break down immediately but there exists a time interval between the application of the critical voltage and the discharge across the electrodes, This time interval is of an indeterminable nature and may be a period from Zero to five minutes or more in duration. Itis apparent therefore that such arresters may or may not properly protect a system of distribution from over voltage conditions dependent on how long the time interval hap- .Y pens to be before the gap discharges and relieves the system.

After extensive experiments, I have found that the cause for this time delay may be explained theoretically as follows: It is a well known theory that a spark gap breaks down upon the application of critical voltage by the movement of ions within the gap with such velocity that they strike gas molecules and form other ions which in turn collide with still other moleculesy to form still more ions until iinally the gap breaks down. This theory is known as the ioniza tion by collision theory for the break down of spark gaps and depends upon the occurrence of at least one ion within the influence of the spark gap when the requisite voltage is impressed across the gap. In a vessel containing a rarefied atmosphere or a vacuum, it is apparent that fewer ions are present within the vessel than if the vessel contained air and the possibility of one or more of the ions present being within the vicinity of the spark gap and under the infiuence of the field produced by the applied voltage is therefore more remote. According to the ionization by collision theory, therefore, the indeterminate character of the time delay between the application of critical voltage and the break down of the gap can be explained by the fact that an ion may or may not be present within the vicinity of the gap when the proper voltage 1s applied. If an ion or ions is present within the vicinity of the gap, when the critical voltage is applied a discharge occurs immediately, whereas if no ions are present, it takes an indeterminate time before such ion or ions within the evacuated vessel comes within the vicinity of the spark gap or is brought within such vicinity by the eld set up between the electrodes of the spark gap by the applied voltage.

I have found that this indeterminate time lag in the discharge of arresters of the vacuum type can be eliminated by removing the probability of an ion being absent within the vicinity of the gap. This probability is removed by placing within the evacuated chamber in proximity to the gap a small amount of a substance or material which is continually giving ofi` ions. Such a substance may be any radioactive material but I preferably use a small amount of a solution of radium chlorid. The presence of radioactive material within the evacuated vessel of the arrester is continually undergoing an yionic discharge not only giving off ions but also giving off the well known emanation which fills the evacuated vessel and itself produces ions so that there exists, therefore, an abundance of ions within the vessel and within the vicinity of the spark gap. When, therefore, the critical voltage is applied to the gap which is constantly ionized, there is an immediate discharge of the gap according to the ionization by collision theory with the entire elimination of any time lag or delay.

The total time delay between the application of critical voltage and the break down of the spark gap is made up in reality of two separate time lags. The greatest lag is that of the indeterminable character just described while the other lag is relatively small and is a function of the ionic saturation of the spark gap, that is, accordingto the ionization by collision theory, it will take a longer time for the gap to break cally eliminate the shorter time lag.

I am aware that radioactive material has been used in proximity to a spark gap in air to cause a lowering af the voltage at which the gap will discharge and I am also aware that it is old to use radioactive material within mercury arc lamps and rectiiiers to enable lower voltage to initially start the arc but these problems bear no relation to the problem to be overcome in vacuum arresters. 'llhc phenomena of the time delay which is of indeterminate duration, between the application of break down voltage and the discharge of the gap, 1s

peculiarly characteristic of lightning arresters which have a spark gap in an attenuated atmosphere.

In Fig. 1 of the drawings, l have shown my invention applied to a lightning arrester of the vacuum type. The type of arrester which I have shown as embodying my invention is well known and is disclosed in my patent application, Ser. No. 7 53,17 9. This arrester comprises a hollow metal tube 1 within which is placed a metallic electrode 2 preferably of the disk type and connected to a metal rod 3 extending outside the tube l. The electrode 2 is spaced away from the tube l, which forms the other electrode, to form a spark gap concentric with the electrode 2. The electrode 2 and connecting rod 3 are sealed into the metal tube by means of a seal which is of a character to make a good bond between the metallic surfaces of the tube 1 and the rod 3 and which is suiliciently elastic to withstand the normal changes of temperature without cracking and which is sufficiently impervious to maintain an attenuated atmosphere in the tube 1. ample, as comprising alternate layers of high and low melting point material 4f and 5 respectively and a plug 6 of refractory material such as porcelain. Above the seal and below the electrode 2 is placed a bushing 7 of material such as porcelain or a special glass which is especially adapted to withstand arc dischargeswithout chipping In order to protect the inner surface of the metal tube l, I have secured thereto a sleeve 8 of non arcing metal.

In the upper inturned portion of this shield I place a very small amount of my radio active material 9 which is continually discharging ions into the vicinty of the Such a seal is shown, for eX- spark gap between `the electrodes 1 and 2 and continually giving off an emanation which maintains an ionized atmosphere in the tube. This material may be placed in many other places within the tube l but as a convenient place, I have adopted the location mentioned.

The tube 1 is evacuated to the' desired vacuum through a capillary opening 10 in ythe depression 1l at the top of the tube and then this opening is sealed by filling the depression with a fusible material 12 which may be a low melting point solder. In order to prevent the material 12, should such become melted during the heat of discharge, from passing into the arrester and short circuiting the spark gap, I provide immediately beneath the capillary opening 10, a diaphragm '13 which has capillary openings through the protuberances 14 and which will prevent any material 12 from injuring the arrester.

This arrester, as described, is a unit struc ture which as shown in Fig. 2 may be removably positioned within suitable spring terminal clips 15 and 16 which are mountcd on an insulating base 17 to connect the two electrodes 1 and 2 of the arrester simultaneously to line and ground. The clip 15 is shown, for instance, as connecting'the electrode 2 through conductor 18 to the line conductor 19 to be protected and clip 16 as connecting the tube or electrode 1 by means of conductor 2O to ground, so that I provide a path from the line conductor 19 to ground including the spark gap between electrodes l and 2.

An arrester having a spark gap in a vacuum and embodying my invention will immediately relieve the line conductor of any over voltages which are of an amount equal to or above the critical voltage of the spark gap by causing the immediate break down of the spark gap and the conduction of the over voltage to ground whereas with vacuum arresters of the ordinary type the occurrence of an over voltage on the conductor to be protected which is equal or in excess of the actual voltage necessary to break down the spark gap, will cause the gap to discharge in an indeterminable time depending on the probability of an ion being present within the vicinity of the gap. There is, therefore, a great possibility that they arrester may not relieve the line in time to prevent damage to apparatus.

It is understood that my invention is not restricted to any one type of vacuum arrester but is applicable to all arresters having a spark gap in an evacuated vessel or chamber.

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, a spark gap within said vessel,

2. A protective device com rising an evacuated vessela spark gap wit 'n said vessel, and means coperating with said gap vfor eliminatin Athe time lag between the apgli- 1scation of' reak down voltage and the charge across said gap.

3. A protective device comprising an evacf,

uated vessel, a spark ga within-said vessel, and radioactive materi within said vessel for eliminatin the time lag between the application of reak down potential and the discharge of vsaid spark gap.` L f 4. The combinatlon with a line conductor to be protected, of a path to ing a spark gap, an evacua' which continually introducing into the yvicinity of und includvessel within said` gap 1s located, and' mseans` 4for my, hand said gap a supply of ions to cause the immediate discharge of the gap upon application thereto of break` down voltage.v

5. In vcombination vwith a to be protected, kof means for immediately relieving said line of abnormal voltages comprising ay spark gap connected in a ath betweenl said hne and, ground, a vesse in- .closing said spark gap and containing an attenuatedatmos here, and radioactive material within constant supply of ions within the vicinity of said p and thereby, eliminat' the time lag etween the application of reak down voltage lacro sald gap and the, discharge of said p. f A

Inwitness w ereof, I have hereulonset this 28th day of January, 1:916. 'GEORGE' FRANCIS GRAY. I

vessel for Vmaintaining aV 1in@ conductor

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