US1735114A - Short-circuiting device - Google Patents

Description

Nov. 12, 1929. E. J. HAVERSTICK 3 ,11

SHORT CIRCUITING DEVICE Filed May ;9z7

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INVENTOR Earl J Ha versf/c/r ATTORNEY Patented Nov. 12, 1929 UNITED STATES PATENT OFFICE EARL J. HAVERSTICK, OF OAKMONT, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA SHORT-CIRCUITING DEVICE Application filed May 19,

My invention relates to circuit-making and breaking devices and specifically to short-circuiting devices for series lighting circuits or the like and is a continuation in part of my copending application Serial No. 151,692, filed November 30, 1926, and assigned to the WVestinghouse Electric and Manufacturing Company.

One object of my invention is to provide means for effectively short-circuiting a lamp or other device in case of an interruption of the circuit through the lamp.

A second object of my invention is to provide a cutout that will reliably breakdown at a comparatively low voltage. v

Another object of my invention is to provide a device of the above-indicated character having means embodied therein for regulating the voltage at which breakdown will occur.

Another object of my invention is to provide a cutout such that ordinary variations in operating temperatures will not materially change the value of the breakdown voltage.

A further object of my invention is to provide a cutout that will not short-circuit through the device when subjected to a surge caused by the release of bound charges in a line, such as a lightning stroke.

Heretofore, devices for similar purposes that operated at comparatively high voltages have been used, but such devices were not suitable for circuits of less than about 350 volts. Such devices were those consisting of a varnished fabric inserted between two electrodes. The fabric would puncture and establish contact between the electrodes at a comparatively high voltage and was useful only in a higl1-voltage circuit. Furthermore, it could not be made to regulate closely the voltage at which breakdown occurred in operating conditions.

My invention provides a device'that may be made to operate at a relatively low voltage, such as 50 volts. The value at which the breakdown will occur may be closely regulated, and changes in temperature on account of varying operating conditions do not materially affect the breakdown voltage.

4 When graphite is placed between the elec- 1927. Serial No. 192,557.

trodes of different potential a leakage will occur. I have found that if two discs about one-half inch in diameter are used as electrodes, and a paper spacer which is coated with graphite and provided with a 3/64 inch opening is disposed between the two discs or electrodes, a'leakage of the order of one milliampere will occur when the potential between the electrodes is 25 to 30 volts. I have found upon increasing the voltage that the leakage increases. With the increase in leakage, the graphite conducts a small but a slightly increased amount of current and is warmed thereby.

Since graphite has a negative temperature coclficient of resistance, the conductivity will increase directly as the temperature. Consequently further increases in current will continuously increase the temperature and conductivity of the graphite more and more. It is believed that the cumulative efiects of temperature and conductivity mutually increase with the increased voltage until a conducting medium suflicient to cause a breakdown between the plates is formed in the opening and in the structure enveloping the same. When even a slight rupture occurs an amount of current suflicient in many instances to form a metallic path between the two electrodes will almost instantly result in a complete short circuiting of the electrodes. The complete operation of heating and short circuiting usually occurs in about a half cycle.

I have discovered that the breakdown voltage for a spacer having openings or apertures coated with graphite is influenced by the specific gravity of the graphitic liquid used for coating the spacer and by the thickness of the spacer and by the type of material used in making the spacer. I have found that the breakdown Voltage increases with a decrease of the specific gravity of the coating liquid. When the liquid is too concentrated, it results in an erratic behaviour of the device. I prefer to use a specific gravity of about 1.035, although variations in the specific gravity of the graphite suspension can be utilized with success.

I have found that an increase in thickness of spacer results in a corresponding increase material.

in the breakdown voltage. I prefer to limit the thickness of the spacer to 3 to 10 mils for low voltage series lighting service. The type of paper used influences the breakdown voltage. The coating solution will penetrate a porous paper more completely than it will non-porous or impervious paper, and m N graphite will be distributed throughout the orous paper and on the surface thereof. Vhen porous paper is coated with the graphite suspension, the structure is apt to be flaky and the coating lacks adherence. A greater leakage and a lower breakdown voltage will be required for a porous impregnated paper than for a coated impervious paper of equal thickness. Since the leakage of current is greater and the breakdown voltage is smaller and less constant with increasing amounts of graphite between the plates, I prefer for most purposes to utilize a non-porous paper upon which the coating of graphite can be easily regulated and the leakage limited largely to the surface coating.

The breakdown voltage may be controlled by increasing and decreasing the size of the opening. I prefer to utilize openings of 3/ to 3/ 16 inch in diameter. Within these limits there is a variation in breakdown voltage of approximately volts.

I have found that a most efficient means of controlling the breakdown voltage is to vary the thickness of the washer and the specific gravity of the graphite coating solution.

If the breakdown voltage of one cut-out disc is too low, the breakdown voltage may be increased by inserting a plurality of the treated'paper discs between the terminals, the breakdown voltage being varied according to the number of discs employed.

My invention may best be understood by reference to the accompanying drawings, in which,

Figure 1 shows a greatly enlarged exploded sectional view of one modification of my .shortcircuiting device,

Fig. 2 shows a similar view of another modification of my device, and

Fig. 3 is a diagrammatic view showing a preferred manner of utilizing my invention.

The preferred form of my invention is shown in Fig. 1. Two conducting plates, 1 and 2, of aluminum or other electrically con ducting material are separated by a perforat ed Washer-like spacer 3 of mica, asbestos, cloth, paper or other similar non-conducting I have found a close grained or substantially impervious paper to be the most satisfactory for use as a spacer material. As previously stated, the paper disc has a diameter of the order of one-half inch and a thickness of the order of 3 to mils. 1111 opening 4 about 3/64 of an inch in diamet r, is provided in the disc, and the upper surface 5 and the opening 4 are coated with graphite 6. The

age to the lamps.

graphite also covers a portion 7 of the lower side of the spacer 3, thus providing a contact with plate 2.

In making the type of cut-out described above, I prefer to use a strip of paper of suitable width and punch the holes at along the strip at a distance of about 3/4 inch apart. The strip of paper is then dampened and coated with water suspension of graphite, such as aquadag of a specific gravity of about 1.035. Discs of the desired dimensions, each having an aperture at its center, are then punched from the strip. I have found that aquadag is the most suitable conducting material, but that other materials of a similar nature, such as a metallic paint, wl ich consists of metal particles suspended in a vehicle, printers ink or india ink, may be used. The edge of the spacer is coated with a suitable adhesive material, such as shellac, and the two aluminum electrodes are then placed on either side of the spacer and electrical contact of graphite and electrodes is secured by pressing the discs and spacer together, thus forming a unitary structure. An alternative method of constructing the apertured disc is to coat a strip of paper, or the like, with a solution of aquadag and punch the apertures and discs out of the strip while the strip is supported on a soft block, so that the aquadag will be forced through the opening and caused to coat the margins thereof.

Another modification of my device is shown in Fig. 2. The spacer 13 is a disc of cloth, having threads 14, paper or the like, the fine openings of which form the apertures in which the graphite 15 is placed. In order to coat the cloth and to obtain .a material which will be integral with the cloth, I prefer to use a suspension of graphite in water of about 1.035 specific gravity. The out-out device 15 assembled by placing the treated cloth be tween the plates 1 and 2, coating the edges with shellac and applying pressure as before.

My invention may be utilized in lamps that are associated with a constant current series lighting system, as shown in Fig. 3. For example, lamps, 21, 22,23 and 24 normally operating at volts, are connected in a branch line 25 through series transformers 26, 27, 28 and 29. Tl e branch line may be connected to the secondary winding of a constant current transformer 32, the primary winding 33 of which is connected across the main line 34 and 35. The cut-out devices 36, 37, 38 and 39 are placed in the secondary branch line circuits across the terminals of the lamps 21, 22, 23 and 24:.

The lamp transformers 26, 27, 28 and 29 are so proportioned as to deliver the proper volt- W'hcn an interruption such as the rupture of the filament of lamp 21 oc curs, the voltage of thesecondary branch line 40 across the terminals of the eutout device increases until the cut-out '36 breaks down and short-circuits the lamp 21 and the secondary winding of the transformer 26. Thus, the cut-out prevents the voltage across the terminals of the secondary winding of the transformer from rising to a destructive amount as the breakdown reduces the voltage to substantially zero.

When using a graphite suspension of a given specific gravity, the voltage at which breakdown will occur may be increased by using a thicker spacer or a smaller opening or both. Conversely, if the spacer is made thinner, or the opening is made larger, the breakdown voltage will be decreased.

The breakdown voltage of the second modification of my device may be controlled by increasing or decreasing the thickness of the cloth, by varying the specific gravity of the suspension of graphite and by varying the porosity of the cloth or spacer.

I have found that a discharge occasioned by the release of a bound charge, such as lightning, does not rupture the cut-out devices which I have described and that the device may be made susceptible to breakdown voltages approximately 50 volts, although the breakdown voltage may be varied at Wlll.

Other materials than graphite may be used to make the covering of the spacer provided that the coating produced on the spacer has an extremely small conductivity. Such a material as boron which has a negative temperature coefficient of resistance, and powdered gums and resins which likewise provide a small leakage and have a negative temperature coeflicient of resistance may be substituted for the graphite and used alone or in conjunction with other materials of greater or less conductivity.

It is to be understood that the device which I have shown and described, and its utility in connection with lighting devices is illustrative of my invention and that modifications may be made therein, without departing from the spirit and scope of my invention as defined in the appended claims.

I claim as my invention:

1. A circuit closing device comprising a plurality of conducting bodies, an apertured spacer disposed therebetween and particles of a material having a small conductivity disposed on the margin of said aperture and surrounding said aperture on both the top and bottom surfaces of said spacer.

2. A circuitclosing device comprising a plurality of conducting bodies, an apertured spacer disposed therebetween and particles of material having a negative coefiicient of resistance disposed in said a erture and surrounding said aperture on both the top and bottom surfaces of said spacer.

3. A circuit closing device comprising a. plurality of conducting bodies, an apertured spacer disposed therebetween and particles of carbon disposed on the edge of said aperture and surrounding said aperture on both the top and the bottom surfaces of said spacer.

4. A circuit closing device comprisin a plurality of conduction bodies, a high resistance spacer having a thickness of 3 to 10 mils disposed therebetween and particles of graph ite disposed on an edge of said spacer and on the top and bottom surfaces of said spacer immediately adjacent to said edge.

5. A circuit closing device comprising a plurality of conducting bodies, an apertured spacer disposed therebetween and graphite disposed in said aperture and surrounding said aperture on both the top and bottom surfaces of said spacer to form a high resistance leakage path between the conducting bodies.

6. The method of making a circuit closing device comprising cutting apertures in a sheet of spacing material, coating the sheet of spacing material with a graphitic carbon, cutting a disk from the sheet, having an aperture therein, coating the edge of the disk with adhesive material, placing conducting bodies, one on each side of the disk, and applying pressure.

7. The method of making a circuit closing device comprising cutting an aperture in a sheet of spacing material and applying a coating of a high-resistance material to one side of the sheet in such manner that the coating adheres to the edges of the aperture and to a small portion of the other side of the sheet immediately surrounding said aperture.

In testimony whereof, I have hereunto subscribed my name this 10th day of May, 1927.

EARL J. HAVERSTICK.

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