US1653375A - Protective device - Google Patents

Description

Dec. 20, 1927.

B. E. SHA CKELFORD ET AL PROTECTIVE DEVICE Filed Feb. 15. 1921 INVENTORS BENJH M/N E. SHHCKELFOED WILL/HM H- 7: HOLDEN.

ATTORNEY Patented Dec. 20, 1927.

UNITED STATES v 1,653,375 PATENT OFFICE.

BENJAMI N ESTILL SHACKELFORD, OF EAST ORANGE, AND WILLIAM HENRY TOWNE HOLDEN, OF BLOOMIIELD, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE' LAM? COMPANY, A CORPORATION OF PENNSYLVANIA.

PROTECTIVE DEVICE.

Application filed February 15, 1921. Serial No. 445,247.

Our invention relates to protective devices and more particularly to devices for protecting electrical circuits from high-potential discharges or high-tenslon sources likely to prove dangerous to life or destructive to property. I

, More specifically our invention relates to protective devices of the type 1n whlch refractory electrodes are enclosed in an envelope containing a rarifiedgas. D

An object of our invention is the provlsion of a protective device having greater current-carrying capacity than those heretofore in use.

Another object of one form of our invention is to provide means for automatically grounding the circuit when the gaseous pressure in the device exceeds a predetermined value, thus affording protection against voltages in excess of those desired to be passed over a line, even when the gaseous pressure in the device is too high to pass a discharge.

Although inert gases have heretofore been used in protective devices of the rarifiedgas type to reduce the resistance of the electrode gap, such gases have proved unsatisfactory in performing this function for the reason that the current discharge from the circuit to be protected by devices of this type is small. y

We have discovered that, if the electrode gap contains a mixture of certain gaseous substances, at least one of which is a gas of low dielectric cohesion, such, for instance, as mercury vapor, the current discharge is comparatively large, whereby a greater degree of safety is afforded to the circuit to be protected.

A convenient way of furnishing the metallic vapor'to the electrode gap is to provide a pool of mercury, either within the envelope or in a side tube communicating therewith; the communication of the side tube with the envelope being preferably retained, although, in some cases, it may be desirable to seal or tip off the side tube in the manner usually employed in tipping off an incandescent lamp.

In the preferred arrangement in which the source of mercury vapor is in communication with the electrode enclosure, a pool furnishes a supply from which the vapor of mercury may be evolved.

A mixture of certain gases and vapors has peculiarities that adapt it especially to use in a protective device of the type herein contemplated. It has been found that a mixture of a metallic vapor and a monatomic gas is particularly suitable. The amount of metallic vapor actually present before the discharge begins is small, owing to the low vapor pressure of even volatile metals at three millimeters of mercury, the addition of a drop of mercury raises the pressurerequired to give a sparking potential of 400 volts to about 20 millimeters, while, at the same time, the current in the discharge at any given voltage increases several hundred percent. The resulting device has the advantage of discharging considerable current when the applied voltage is but little in ex' cess of the sparking potential.

It will also be seen that the mixture of metallic vapor and gas has another advantage over a single vapor or gas in that the sparking potential is more definite and less subject to variation, for the reason that the gaseous impurities which may be liberated from the walls of the device by the passage of electric discharges, constitute a smaller percentage of the total pressure of the mixture than of the lower pressure which must be employed when either a gas or a vapor is used singly. It will thus be seen that the presence of the metallic vapor greatly increases the rate of productionof-ions and also lowers the potential required to start ionization by collision and cause a current to flow through the mixture of gas and metallic vapor.

We have further discovered that, if the source of the metallic vapor, which may be a pool of mercury, is spaced from the electrodes, the formation of a mercury arc is prevented. This is advantageous because, should an arc form, the potential drop across the terminals of-the protective device might fall to a value below the normal line voltage of the circuit to be protected, resulting in the persistence of the discharge of the increase in pressure, it is desirable to provide means for short-circuiting the device.

Iir order that the invention may be more fully understood reference is had to the accompanying drawing in which the single figure is a side view of one form of device embodying the invention.

In this View an envelope 9 is provided with a plurality of preferably parallel depending line electrodes 10 and 11 included in, or connected to, the circuit'to be protected, and a grounded electrode 12, preferably located between the line electrodes. The intermediate portions of the pair of line electrodes diverge at 13 and the lower'ends converge at 14, in the manner illustrated, the grounded electrode 12 preferably being a straight wire. The envelope 9 has connected to its lower end one branch of a depending U-shaped fluid-filled tube 15 which communicates with the envelope and has its unconnected end closed.

It. is desirable to employ aliquid substance, since the float elements which form part of this modification require a liquid medium for their operation. The liquid should, however, be of such character as to furnish a vapor which will decrease the resistance of the electrode gap sufiiciently to cause the circuit to be protected, as hereinbefore indicated. Mercury fulfills these requirements, since it is liquid and has a comparatively high vapor pressure at ordinary temperatures. Hence, we prefer to fill the U-tube with mercury. It is evident that other substances or mixtures might be used instead of the mercury, as a buoyant medium, although some such substances or mixtures might even require the application of heat to create a sufficient vapor pressure to give satisfactory service. A float 16, comprising a buoyant part 17, is carried on the mercury column in the tube 15. The part 17 has an Lip-standing staff 18,

preferably consisting of wire and carrying a shorting ring 19 at its upper end adapted to short the line electrodes.

While we have shown the short circuiting element in the form of a ring, it is to be understood that any other form, such as a disc, for instance, which bridges the line electrodes, or the line electrodes and the grounded electrode, will suflice. The level of mercury and the length of the staff 18 are adjusted so that the shorting ring 19 takes a position within the diverging and converging parts to permit the bud 'ng element to remain free from, or clear 0 the electrodes when in normal position, and to come into contact with either the diverging or con verging portions when moved upwardly or downwardly, respectively, from this position. The mercury level in the discharge-tube side will either fall when the increase in pressure is on the envelope side of the device or rise when the increase in pressure is on the closed branch side of the U-shaped tube.

In order to ensure the vertical position of the staff 18, its upper end may be conveniently guided on the grounding electrode, in the manner shown in the drawing, in which the shorting ring surrounds the grounded electrode. Other means may, of course, be employed to guide the staff, for example, a guide eyelet might be secured to the upper end of the staff and have sutlicient diameter to slide freely on the grounding electrode; or the staff might be guided in other ways and from other points, particularly in case the grounding electrode should be dispensed with.

Manifestly, instead of the short-circuiting ring being located within the space bounded by the diverging and converging parts of the electrodes, the short-circuiting ring might surround the electrodes and drop down on the diverging parts when the mercury in the U-shaped tube should change its position.

What is claimed is:

1. In a protective device, the combination of a plurality of electrodes, an enclosure for said electrodes having a column of mercury the height of which is regulated by the pressure within said envelope, a float compris ing an electro-conductive portion moi'able with the mercury column and adapted to short circuit said electrodes when the pressure within said envelope reaches a predetermined point.

2. An electric discharge device comprising an envelope containing gaseous filling, a plurality of electrodes in said envelope, a body of liquid contained therein, a float on said liquid and means opcratively associated with said float for short circuiting said electrodes when the pressure within the device reaches a predetermined point. 7

In testimony whereof. we have hereunto subscribed our names this 14th day of Feb ruary, 1921.

BENJAMIN ESTILL SHACKELFORD. WILLIAM HENRY TOWNE HOLDEN.

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