US1763267A - Resistance plate - Google Patents

Description

Patented June 10, 1930 UNITED STATES.

PATENT OFFICE JOSEPH SLEPIAN, O1 SWISSVALE, PENNSYLVANIA, ASSIGNOR 'IO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA RESISTANCE PLATE Application filed April 29,

This invention relates to resistance materials, more especially to a material adapted for use in the auto-valve lightning arresters described in my Patents Nos. 1,509,493 and 5 1,509,497, assigned to the lVestinghouse Electric and Manufacturing Company.

An arrester of the above-mentioned type consists of superposed or stacked plates or disks of a material having a relatively high resistance, said stack of plates being connected between the circuit to be protected and the ground. The adjacent disks are separated by very small spaces having a breakdown voltage of the order of 300 to 500 volts, there being relatively few points of contact.

In operation, a discharge flowing through the disk pile causes breakdown to occur at those points which have the minimum breakdown potential, after which the discharge spreads uniformly over the entire surface of the plates or disks. If the resistance of the points of contact of the plates is not sufficiently high, a considerable portion of the current will flow through said points, causing heating 2 of the same and allowing the line current to pass or lea-k therethrough at a comparatively low voltage, after the abnormal or lightning discharge has passed.

It is among the objects of the present invention to provide a means for preventing the flow of an objectionable leakage current after the lightning discharge has ceased.

It is another ob ect of my invention to devise a method of treating plates or disks of resistance material whereby the characteristics thereof are not changed immediately but whereby the plates automatically increase in resistance when subsequently heated.

In practising my invention, I provide plates of disks of resistance material generally consisting of lamp black, carborundum and kaolin. The ingredients are mixed with water, molded to the desired form and then fired in a furnace to render the body hard and permanent. I then place the plates in a solution of an oxidizing agent of any suitable kind, such as a solution of chromic acid in water. The oxidizing agent should preferabl be non-hygroscopic and, when decomposed: should leave a residue that does not 1922. Serial No. 557,364.

terial depth so that, in use, when the contact points thereof become heated, oxidation may occur at the said points of contact.

The plates are assembled to provide an arrester as usual. WVhen a discharge passes therethrough, and assuming some of the points of contact are of relatively low re sistance, heating will occur at such points owin to the relatively large current passing tlierethrough. The heat renders the oxidizing agent active and causes the same to react with at least part of the carbonaceous material of the plates, oxidizing the same and thus raising the resistance at such contact points. If, under conditions of service, new contact points should be formed or the highresistance contact points already formed should in some way become injured or destroyed, the same reaction will occur as before, raising the resistance of the contact points.

My invention is illustrated in the accompanying drawing, wherein Fig. 1 is a View, partly diagrammatic and partly in cross-section, illustrating a lightnin g arrester embodying my invention, and

Figs. 2 and 3 are enlarged views illustrated ing the contacting surfaces of the plates and the operation thereof.

As shown in Fig. 1, a disk-like or autovalve lightning arrester 1, as described in my aforementioned Patent No. 1,509,493, comprises a pile of plates or disks 2 of the composite resistor material hereinabove described, held within a casing 3 under a compression exerted by a spring 4. The lightning arrester is connected between a line wire 5, to be protected, and a ground connection 6. A small series gap device 7 may be included in circuit with the lighting arrester for a purpose to be mentioned later.

Although the disks 2 are ground smooth, there are certain small irregularities 1n the surfaces, so that the contacting surfaces are, in reality, touching at only a relatively few contact points 8, of small area, as shown in Figs. 2 and 3. The plates are separated, for the most part, by small spaces const1tut1ng glow-discharge gaps, which usually are not over 8 mils in length.

When an excessive voltage appears on the line 5, the short series gap 7 readily arcs over, and a glow-discharge is in1t1ated between each pair of the disks 2, at points which are separated by the optimum gap length of about mil, the discharge rapidly spreading, from such points, to uniformly cover the entire area of the opposed disk surfaces, as indicated by the uniformly spaced arrows in Fig. 3. The extremely high resistivity of the composite resistor material of the disks prevents the concentration of heavy currents at any point, which would form a hot spot causing the development of a low-voltage are, as distinguished from a glow discharge which has a voltage-drop of the order of 300 volts.

When the excess-voltage disturbance has passed, the glow-discharge ceases, and the only current-flow is that which passes through the high-resistance contact points 8, as indicated in Fig. 2, and even this trifling leakage current may be cut off by the utilization of the small series gap 7 across which an arc can not maintain itself with such small currents.

It will be seen from the above description of my invention that plates made in accordance therewith are very effective in providing a material which has a moderate resistance throughout the body thereof so as not to unduly limit the current-carrying capacity thereof and having, at the same time, a sufficiently high contact resistance to prevent an appreciable leakage current from passing therethrough. The method of treating such plates is very simple and the materials used are relatively inexpensive; and I have been enabled to produce plates by this method which are impregnated uniformly and have resistances of approximately the same amount. This method, therefore, lends itself very readily to quantity production.

Although I have stated that I utilize chromic acid in the method, it is apparent that other oxidizing agents of suitable nature may be used in place thereof. For instance, I may use potassium chlorate, permanganic acid or other suitable oxidizing agents. It is desirable that the oxidizing agent used should be inactive at ordinary temperatures, such as are encountered in practice and should not deteriorate over a fairly long period of time. The oxidizing agent should become active at a. relatively low temperature, in order to avoid such copious electron-emission as would result in the establishment of an arc, as'distinguished from a glow discharge, but the oxidizing temperature should be sufliciently above the normal operating temperatures of the lightning arrester to insure that there shall be no danger of slow oxidation taking place normally. I have found that an oxidizing agent which freely oxidizes carbon at 100 degrees to 200 degrees (3., is suitable for my purpose, such temperatures being below the temperature at which air acts on the composite resistor material to oxidize the carbon therein, the objection to such air oxidation being that it is very uncertain in its action and produces a high resistivity in some spots and a relatively low resistivity in others.

I preferably utilize the oxidizing agent in solution and thoroughly impregnate the plates therewith but it is not essential that the oxidizing agent be in solution, since it may be applied in various other ways. As above explained, it is not necessary that the oxidizing agent shall extend throughout the body of the plates but need cover the contact surfaces of the plates only. Only a relatively small amount of the oxidizing agent is necessary and I generally utilize an amount suflicient to completely oxidize the carbon in the material, the amount of the carbon being generally about 4% or less, producing a composite resistor material having a conductivity which is only an exceedingly small fraction of the conductivity of carbon. It is to be understood that, although I may add a sufficient amount of the oxidizing agent to accomplish the oxidation of all the carbon, such complete oxidation never occurs in practice and I merely add such amount out of an abundance of precaution.

The methods of making and treating resistor bodies, described herein, constitute the subject-matter of my divisional application, Serial No. 668,552, filed October 15, 1923.

I claim as my invention:

1. A composite resistor material of which the resistance may be changed by heating comprising a finely divided oxidizable conducting substance distributed throughout a substantially non-conducting mass and characterized by having incorporated therein an oxidizing material capable of oxidizing said finely divided oxidizable conducting substance under abnormal temperature conditions obtaining in operation.

2. A composite resistor material of which the resistance may be changed by heating comprising a finely divided oxidizable conducting substance distributed throughout a substantially non-conducting mass and characterized by having incorporated therein a non-hygroscopic oxidizing material capable of oxidizing said finely divided oxidizable conducting substance under abnormal temperature conditions obtaining in operation.

3. A composite resistor material of which the resistance may be changed by heating, comprising an oxidizable conducting substance distributed throughout a substantially non-conducting mass, and characterized by having an oxidizing material incorporated therein, said oxidizing material being capable of exerting a substantial oxidizing action on said oxidizable substance only at temperatures higher than normal operating temperatures.

4. A composite resistor material of which the resistance may be changed by heating, comprising an oxidizable conducting substance distributed throughout a substantially non-conducting mass, and characterized by having an oxidizing material incorporated therein, said oxidizing material being capable of exerting a substantial oxidizing action on said oxidizable substance only at temperatures higher than normal operating temperatures, and leaving a residue having a conductivity substantially difi'erent from that of said oxidizable conducting substance.

5. A composite resistor material of which the resistance may be changed by heating, comprising an oxidizable conducting substance distributed throughout a substantially non-conducting mass, and characterized by having an oxidizing material incorporated therein, said oxidizing material being capable of exerting a substantial oxidizing action on said oxidizable substance only at temperatures higher than normal operating temperatures, and leaving a substantially non-conducting residue.

6. A composite resistor material of which.

the resistance may be changed by heating, comprising an oxidizable conducting sub stance distributed throughout a substantially non-conductin mass, and characterized by having an oxldizing material incorporated therein, said oxidizing material being capable of exerting a substantial oxidizing action on said oxidizable substance only at temperatures higher than normal operating temperatures but being efl'ective at a temperature below that at which air acts on the composite resistor material to oxidize said conducting substance. I

7. A composite resistor material of which the resistance may be changed by heating, comprising an oxidizable conducting substance distributed throughout a substantially non-conductin mass and characterized by having an oxidizing material incorporated therein, said oxidizing material being capable of exerting a substantial oxidizing action on said oxidizable substance only at temperatures higher than normal operating temperatures but being eflective at moderate temperatures of the order of 200 C.

8. A composite resistor material containing fineliy; divided carbon distributed throughout a su stantially non-conducting mass and characterized by being impregnated with chromic acid.

9. A composite resistor material containing finely divided carbonaceous conducting particles distributed throughout a substantially non-conducting mass and a soluble oxidizing impregnating agent therein operative to oxidize some of said carbonaceous conducting particles to increase the resistivity of said composite material. 10. A composite resistor material containing finely divided carbonaceous conducting particles distributed throughout a substantially non-conducting mass and an oxidizing agent therein operative to oxidize some of said carbonaceous conducting particlesto increase the resistivity of said composite material only at temperatures higher than ordlnary operating temperatures therein.

11. An electric device including a pair of juxtaposed bodies each comprising a composite resistor material containing a finely divided oxidizable conducting substance distributed throughout a substantially non-conducting mass and an oxidizing agent in the eflective surfaces of said bodies capable of oxidizing said finely divided oxidizable conducting substance to increase the resistivity thereof at points of excessive heating.

12. A composite resistor material containing finely divided conducting particles distributed throughout a substantially non-conducting mass and a chemical reagent therein operative on some of said conducting particles to alter the resistivity of said composite material only at temperatures higher than ordinary operating temperatures therein.

13. An electric-device including a pair of juxtaposed bodies each comprising a composite resistor material containing a finely divided conducting substance distributed throughout a substantially non-conducting mass and a chemical reagent in the effective surfaces of said bodies capable of reacting on said finely divided conducting substance to produce a substance of increased resistivity at points of excessive heating.

14. A composite, high-resistance material comprising a binding and filling material, a finely divided soluble impregnating oxidizing material and a finely divided conductor material of a nature adapted to be acted upon by said oxidizin material.

15. A composite, high-resistance material comprising a binding and filling material, a finely divided oxidizing material and a finely divided conductor material of a nature adaptedto be acted upon by said oxidizing material at temperatures above normal operating temperatures.

16. A composite, high-resistance material comprising a binding and filling material, a finely divided solub e impregnating oxidizing material and a finely divided conductor materialofanatureadapted to be acted upon by said oxidizing material at temperatures above normal operating temperatures, said binding and filling material being of a nature requiring heat treatment at an elevated temperature, and said oxidizing material being substantially inoperative at normal operat ing temperatures but being decomposable at a temperature lower than that required in the aforesaid heat treatment of said binding and filling material.

17. A composite resistor body capable of copious electron-emission at an elevated temperature and including a binding material and finely divided oxidizable conducting substances distributed in the mass of said body, and means for oxidizing said substances at temperatures higher than the normal operating temperature but below the temperature of copious electron-emission.

18. A di barge-gap electrode comprising a discharge surface of a composite resistor material including conducting particles dis tributed throughout a substantially non-conducting mass, and means for causing an oxidation of said particles upon excessive heating of the same.

19. A discharge-gap electrode comprising a discharge surface of a composite resistor material including conducting carbonaceous particles distributed throughout a substantially non-conducting mass, and means for causing an oxidation of said particles at the points of excessive heating.

20. A lightning-arrester comprising a plurality of composite resistor bodies disposed close to each other to constitute minute gaps having a breakdown voltage of the order of 300 to 500 volts, said composite resistor bodies comprising conducting particles and an oxidizing agent distributed throughout a substantially non-conducting mass, said oxidizing agent being, substantially inactive at normal operating temperatures, but being sufficiently active on said conducting particles at temperatures below the temperature of copious electron emission to cause a material increase of the resistivity of said resistor bodies at points of excessive heating.

21. A lightning-arrester comprising a plurality of composite resistor bodies disposed close to each other to constitute minute gaps having a breakdown voltage of the order of 300 to 500 volts, said composite resistor bodies comprising carbonaceous conducting particles and chromic acid distributed throughout a substantially non-conducting mass.

22. A lightning-arrester comprising a plurality of composite resistor plates disposed substantially in contact with each other to constitute minute gaps between the plate surfaces, said composite resistor plates includingafinely dividedconducting substance having a negative temperature coeflicient of resistance distributed throughout'a substantial- 0 of April 1922. 8

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