US2162949A - Protective device for electric circuits - Google Patents

Description

June 20, 41939. L, o. GRONDAHL PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Filed Oc't. 13, 1938 HIS ATTORNEY Modif Maia/ I Selemam Patented June 20, 1939 UNITED STATES PATENT OFFICE PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Application October 13, 1938, Serial No. 234,812

29 Claims.

My invention relates to protective devices for electric circuits.

Electrode units comprising a plurality of different intimately united substances, one of which is a semi-conductor, and possessing the characteristic of offering a relatively high resistance to the ow of current through the units in at least one direction for potentials below a certain critical potential, and a relatively low resistance for potentials above said critical potential are well-known in the art. One such unit which may be mentioned comprises a layer of copper having formed thereon a layer of copper oxide the outer surface of which is coated with one or more thin layers of metal to facilitate making contact therewith. Another such unit comprises a supporting or backing plate of any suitable metal such as iron or brass, a layer of nickel in contact with said backing plate, a layer of selenium in contact with said nickel layer, and a layer of gold, silver, tin, solder, Woods metal or the like in contact with the selenium layer.

In experimenting with units of this type, I have found that when one of these units is subjected to a potential surge which exceeds the critical potential necessary to break down the normally high resistance which the unit offers to the flow of current in one direction, the heat generated by the current flow at the relatively small spot or spots at which the breakdown occurs tends to vaporize the semiconductive layer and the associated'thin contact layer, and if this vapor is permitted to escape freely, the spot or spots at which the breakdown occurs will be left open circuited following the shock, so that the high resistance which the unit normally oiers to current flow will be restored. Furthermore, if successive shocks are given to such a unit, the semiconductiveI layer and associated contact layer will become punctured in one or more diierent spots each time, and so long as the vapors are free to escape, the puncture will leave the unit uninjured at least until a relatively large number of shocks have been given to the unit.

One object of my invention is to provide means for securing contact with the contact layer of a unit of the type described in a manner which will permit the vapors formed by the flow of current when the unit breaks down due to a voltage surge to escape freely, and which will at the same time enable the unit to be readily connected with any suitable circuit to cause it to serve as a lightning arrester.

Another object of my invention is to provide a lightning arrester which is particularly suitable for, although in no Way limited to, use in low voltage circuits.

A further object of my invention is to provide a lightning arrester which will be inexpensive to manufacture, reliable in operation, and have a long life without the necessity for frequent repair.

Other objects and characteristic features of my invention will appear as the description proceeds.

In the accompanying drawing, Fig. l is a vertical sectional view showing one form of lightning arrester embodying my invention. Fig. 2 is a sectional view taken on the line II--II of Fig. 1. Fig. 3 is a view similar to Fig. 1 showing a modied form of lightning arrester embodying my invention. Fig. 4 is a View similar to Fig. 1 showing another form of lightning arrester embodying my invention.

Similar reference characters refer to similar parts in each of the several views.

Referring first to Figs. 1 and 2, the lightning arrester in the form here shown includes an electrode unit A comprising a disc or plate I provided on both sides with a layer 2 of cuprous oxide having a thickness depending upon the voltage at which it is desired to have the arrester break down. Each oxide layer 2 may be formed on the mother copper in accordance with any of the Well-known processes employed in the manufacture of copper oxide rectifier elements, and inasmuch as the particular method employed is not material to my present invention, it is believed to be unnecessary to describe it in detail herein. intimately associated with the outer surface of each oxide layer 2 is a thin layer 3 of a suitable conducting metal, which in the particular embodiment of my invention here illustrated comprises electrolytically reduced copper, and intimately associated with the outer surface ofA each copper layer is another thin metallic conducting layer 4 which may, for example, comprise electrolytically deposited nickel. The method by which the layers 3 and 4 are formed on the unit likewise comprises no part of my present invention and may, for example, be similar tov that described in an application for Letters Patent of the United States, Serial No. 225,369, filed by Philip H. Dowling on August 17, 1938, for Electrical rectiers.

It should be pointed out that While the unit A asshown in the drawing is provided with a layer of electrolytically reduced copper and a layer of electroplated nickel to facilitate making contact with the cuprous oxide layer, satisfactory contact can be made with the oxide layer by means of other thin metallic layers. For example, the

reduced copper without .the nickel can be used, or the reduced copper can be sprayed with a thin 'coat of some other metal such as solder, tin or Woods metal, or contact with the oxide can be made by spraying or evaporating a layer of annthermetal directly onto it.

The unit A is provided with a centrally located opening or hole 5 and is mounted on a clamping bolt 6 from which it is insulated by an insulating sleeve l. Disposed on opposite sides of the unit in contact with the nickel layers i are contact -members 8 which may have any desired construction that will provide good contact with the nickel layer, but which at the same time are of such a nature that they will permit vapor to escape freely in theevent the adjacent nickel layer is pierced due `to a voltage surge breaking down the high resistance junction which normally exists in one direction between the copper and the adjacent oxide layer. As here shown, these contact members each comprise one or more coils of ne wire or a mass of iine threadsof any suitable metal such as nickel, nichrome, copper, platinum, silver, gold, phosphor bronze, nickel silver or the like, but these members may, for example, be in the form of a mat or layer of metallic wool made from any of the named metals or any other suitable metal.V It will be noted that these contact members are of such a nature that they engage the adjacent nickel layer at a large number of different spots of relatively small area, but are suiciently pervious that vapors can escape freely through them over the entire face of the nickel layer. This is important because it is desirable that the metallic conducting layers 3 and 4 should be thin, and when these layers are thin it is necessary to make contact with them aft a number of places not too far apart in order to provide sufcient conductance over the surface.

Interposed between the right-hand contact member 8 and the head of the bolt 6 is a conducting plate Ii and an insulating washer I2, and interposed between the left-hand contact member 8 and a nut I3 which is screwed onto the bolt 6 to clamp the parts together is a conducting plate I4 and an insulating washer I5. To assist in holding the contact members 8fJ in place these contact members may, if desired, be secured to the adjacent conducting plates. This may be accomplished, for example, by laying the conducting plates on a horizontal surface with the side to which the conducting members are to be secured facing upwardly, covering their upper surfaces with molten solder, and then inserting the contact members into the solder and allowing it to harden. The two conducting plates I I and I4 have wires I6 and I'I attached thereto to facilitate connecting the arrester with an electrical circuit.

An arrester constructed in the manner described is particularly suitable for use in connection with low voltage circuits, and will serve as a short circuitfor a relatively large. number of successive surges in excess of the critical potential at which the unit breaks down without any seriously detrimental increase in the normal leakage current which, due to the inherently high resistance which normally exists between the two nickel layers of the unit for current of either polarity, will be so small as to be almost negligible. It Vwill be understood, of course, that when a voltage surge in excess of the critical potential at which the arrester breaks down is impressed across the arrester, the resulting current which Ailows will pass through the arrester from one vapor pervious contact member 8 to the other through the one junction between the copper oxide and the mother copper in one direction and through the other junction in the opposite direction, and that the junction through which the current flows from the oxide to the mother copper will not be affected since it normally offers a low resistance to current iiow in this direction but that the other junction will be momentarily destroyed at one or more spots so that it will also offer a low resistance to the current flow. The actual circuit voltage with which the arrester can be used, as well as the voltage at which it breaks down, depends on the method of heat treating the electrode unit during the oxidation process, the thicknesses of the oxide layers, and the amount of ventilation given to the unit, all of which factors can be varied through relatively wide limits. For example, it is possible to provide a unit which is much larger than that necessary for the lightning arrester itself, and' to remove the oxide from that portion of the unit which is not used, so that the outer portion of the unit will extend beyond the remainder of the assembly and will act as a Ventilating n in the manner shown in the drawing. Likewise, the size of the conducting plates ll and Iii can be increased to provide better radiation, although inasmuch as the contact members 8 are not very good conductors of heat it is preferable to obtain the desired heat radiation by increasing the size of the electrode unit. With the electrode unit A constructed in accordance with the teachings set forth in thehereinbefore referred to Dowling application, the arrester can be used on circuits having normal operating voltages up to 6 volts or more, and it will break down on a voltage surge in the neighborhood of 70 volts. It will be seen, therefore, that an arrester constructed in ac. cordance with my invention can be made to provide protection against surges that are too low to break down other types of lightning arresters.

From some applications, particularly where the `circuit which is to be protected is a direct current circuit, the mother copper can be used as one terminal of the arrester and the wires I6 and I'I can be connected together to serve as the other terminal. Or, if desired, the unit A need be oxidized on one side only in which event the conducting plate il or I4 and the adjacent contact member 8 can be omitted from the assembly on the side'which is not oxidized, and the mother copper can be used as one terminal of the arrester. y

If it is desired to use an arrester of the type embodying my invention for higher voltage circuits, this desirable result can be obtained by assembling a suitable number of the electrode units in series in the manner shown in Fig. 2, it being noted that the same type of contact member 8 is provided to obtain an electrical connection with the outer nickel layer of each unit as is provided in Fig. 1 to obtain an electrical connection with the nickel layer of the unit A.

It should be 'particularly pointed out that, while in the form of my invention illustrated in Figs. l and 2 I have shown an electrode unit of the copper oxide type, my invention is not limited to a unit of this specific type, but on the l contrary my invention contemplates the use of any type of electrode unit including a semiconductor united with one or more conductors and possessing the characteristic of offering a normally high resistance in at least one direction for potentials below a certain critical potential and a low resistance for potentials above such critical potential, and which further possesses the characteristic that it will not become shortcircuited when punctured by a voltage surge provided the vapors produced are allowed to escape freely. Another form of unit which may be employed and the method of connecting it in a circuit is shown in Fig. 4. Referring to Fig. 4, as here shown the arrester here illustrated is similar to that illustrated in Fig. l with the exception that the electrode unit A has been replaced by an electrode unit B consisting of a plate or disc 20 of iron, a layer 2| of nickel in intimate contact with each side of the disc 20, a layer 22 of selenium in intimate contact with the outer surface of the nickel layer 2|, and a contact layer 23 of suitable metal such as gold, silver, Woods metal, tin or solder in intimate contact with the selenium layer. An arrester constructed in this manner possesses the same characteristics as an arrester constructed in the manner s'hown in Fig. l, and its operation will be readily understood from the foregoing description Without further detailed description.

It should be observed, however, that for use in certain circuits, particularly those which are subjected to direct current only the arrester can be constructed from an electrode unit which is provided on one side only vwith the nickel, selenium and metal contact layers.

One advantage of a lightning arrester embodying my invention is that it Will function for a large number of lightning discharges without losing its effectiveness as a lightning arrester.

Although I have herein shown and described only a few forms of protective devices for electric circuits embodying my invention, it is understood that various changes and modifications may be made therein Within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A lightning arrester comprising an electrode unit consisting of a layer of a semiconductive substance disposed between and intimately associated with two metallic layers one of which is relatively thin in such manner that said unit possesses the characteristic of offering a relatively high resistance in one direction for potentials below a critical potential and a relatively 10W resistance for potentials above said critical potential, and means for making contact with said relatively thin layer in such manner that vapors produced by the current which flows when a potential in excess of said critical potential is impressed across said unit in said one direction can escape freely, whereby the unit will not become short-circuited due to a high potential discharge. 'Y

2. A lightning arrester comprising an electrode unit consisting of a semiconductive layer disposed between two metallic layers one of which is relatively thin, saidunit possessing the characteristic of offering a relatively high resistance in one direction for potentials below a critical potential and a low resistance for potentials above said critical potential, and a contact member engaging said thin metal layer so constructed that vapors produced by a high potential discharge passing through said unit in i said one direction are free to blow out, whereby the unit will not become short-circuited due to a high potential discharge.

3. A lightning arrester comprising an electrode unit consisting of a semiconductive layer in intimate contact with a backing layer and a relatively thin contact layer, and means for establishing contact with said unit in such manner that vapors formed by a lightning discharge passing through said unit can escape freely.

4. A lightning arrester comprising an electrode unit including a metal layer, a semiconductive layer in intimate contact with said metal layer, and a thin contact layer in intimate contact with said semiconductive layer, and means for making Contact with said contact layer in such manner that vapors formed by a lightning discharge puncturing said contact layer can blow out and escape freely.

5. A lightning arrester comprising an electrode unit consisting of a metal layer, a semiconductive layer in intimate contact with said metal layer, and a thin contact layer in intimate contact with said semiconductive layer, said unit possessing the characteristic of being substantially non-conducting in one direction for potentials below a critical potential and of becoming conducting for potentials above said critical potential, and means pervious to metal vapors in engagement with the contact layer of said` unit for establishing contact therewith.

6. A lightning arrester comprising an electrode unit consisting of a metal layer, a semiconductive layer in intimate contact with said metal layer, and a metalliclm in intimate contact with said semiconductive layer, said unit possessing the characteristic of being substantially non-conducting in one direction for potentials' below a critical potential and of becoming conducting for potentials above said critical potential, and means for making contact with said unit to permit it to be readily connected in an electric circuit including a metallic contact member of such construction that vapors can escape freely through it in engagement with said metallic lm.

7. A lightning arrester comprising an electrode unit consisting of a metal layer, a semiconductive layer in intimato contact with said metal layer, and a metallic lm in intimate contact with said semiconductive layer, said unit possessing the characteristic of being substantially non-conducting in one direction for potentials below a critical potential and of becoming conductive for potentials abovev said critical potential, and means for making contact with said unit to permit it to be readily connected in an electric circuit including a mass of metal wool engaging said metallic film.

8. A lightning arrester comprising 'an electrode unit consisting of a metal layer, a semiconductive layer in intimate contact with said metal layer, and a metallic film in intimate contact with said semiconductive layer, said unit possessing the characteristic of being substantially nonconducting in one direction for potentials below a critical potential and of becoming conducting for potentials above said critical potential, and means for making contact with said metal film so constructed that vapors formed by a lightning discharge puncturing the semiconductive layer and said metallic film can escape freely.

9. A lightning arrester comprising an electrode unit consisting of a metal disc, a semiconductive layer in intimate electrical contact with each side of said metal disc, and a metal contact layer in intimate contact with each semiconductive layer; and a contact member of such a nature that vapors can pass freely through it in engagement with each ycontact layer and comprising means for establishing electrical connection with said unit.

10. A lightning arresterv comprising an aperv tured plate provided on both sides with a semiconductive layer and with a thin metallic contact layer in engagement with the outer surface of each semiconductive layer, a mass of metallic wool in engagement with each contact layer, apertured contact plates disposed adjacent the outer sides of said masses of metallic wool, a clamping bolt passing through said unit and said contact plates for securing the parts together, and means for insulating the parts from said bolt.

11. A lightning arrester comprising a copper disc having formed thereon a layer of copper oxide the surface of which has a layer of another metal in intimate contact therewith, and means for making contact with said metal layer in such manner that vapors formed by a lightning discharge can escape freely.

12'. A lightning arrester comprising a copper body having a layer 'of copper oxide formed thereon, a metallic coating formed on said oxide layer, and means for making contact with said metallic coating in such manner that the vapors formed by a lightning discharge can blow out freely.

13. A lightning arrester comprising a body of copper having formed thereon a layer of copper oxide the surface of which has been reduced to the metallic state and then coated with a layer of another metal, and means for making contact With said metal coating in such manner that vapors formed by a lightning discharge can blow out freely.

14. A lightning arrester comprising a body of copper having formed thereon a layer of copper oxide, a layer of metal in intimate contact with said oxide layer, and means for making contact with said metal layer comprising a body of metal wire engaging said metal layer.

15. A lightning arrester comprising a copper disc having a layer of copper oxide formed thereon, a metallic layer in intimate contact with said copper oxide layer, and a mass of ne wire engaging said metallic layer and comprising means for Amaking contact therewith in such manner that vapors formed by a lightning discharge puncturing said oxide and metallic layers can escape freely.

16. In combination, a copper body having a layer of copper oxide formed thereon, a metallic layer in intimate contact with said oxide layer, and means for making contact with said metallic layer including a mass of wire wool engaging said metallic layer.

17. A lightning arrester comprising a copper body having a layer of copper oxide formed thereon, a layer of electrolytically reduced copper in intimate contact with the outer surface of said oxide layer, a layer of electroplated nickel Yin intimate contact with said reduced copper layer, and a mass of metal of such a nature that it is pervious to vapors formed by a lightning discharge puncturing said copper and nickel layers in intimate contact with said nickel layer to establish an electrical connection therewith.

18. A lightning arrester comprising a copper body Ahaving a layer of copper oxide formed thereon, a layer of metal in intimate contact therewith, and a contact member engaging said metal layer, said member being of such construction that vapors formed by a lightning discharge puncturing said metal layer can escape freely.

19. A lightning arrester comprising a copper bo'dy having a layer of copper oxide formed on both sides thereof, a layer of metal in intimate contact with each oxide layer, and a contact member engagingeach metal layer,4 each said contact member being of such construction that vapors puncturing the adjacent metal layer are free to blow out and leave the area at which the puncture took place open circuited.

20. A lightning arrester comprising a copper body having a layer of copper oxide formed on both sides thereof, a layrer of electrolytically reduced copper in intimate contact with the outer surface of each oxide layer, a layer of nickel electroplated onto each reduced copper layer, and a Contact member engaging each nickel layer for establishing a circuit from one nickel layer to the other, each said contact member being of such co-nstruction that vapors formed by a lightning discharge puncturing the adjacent metal layer are free to blow out and leave the area at which the puncture took'place open circuited.

21. A lightning arrester comprising an electrode unit consisting of a body of copper having a layer of copper oxide formed thereon, and means for making contact with said oxide layer including a layer of metal in intimate contact with said oxide layer and a contact member cooperating with said metal layer, said contact member being of such construction that vapors formed by a lightning discharge puncturing the adjacent metal layer are free to blow out and leave the area at which the puncture took place open circuited.

22. A lightning arrester comprising a copper disc having a layer of copper oxide formed on both sides thereof, a layer of metal in intimate contact with each oxide layer, a clamping bolt passing through said disc, a contact member comprising a mass of metal strands surrounding said bolt adjacent each metal layer and in engagement with the associated metal layer, and a metal contact plate in engagement with each contact member, all of said parts being insulated from said bolt.

23. A lightning arrester comprising a metal plate, a layer of nickelformed on said plate, a layer of selenium in intimate contact with said nickel layer, a contact layer in intimate contact with said selenium layer, and means for making contact with said contact layer in such manner that vapors formed by a lightning discharge passing through said unit can escape freely.

24. A lightning arrester comprising a metal plate, a layer of nickel formed on said plate, a layer of selenium in intimate contact with said nickel layer, a contact layer in intimate contact with said selenium layer, and a contact member pervious to vapors in engagement with said contact layer.

25. A lightning arrester comprising a metal plate, a layer of nickel formed on said plate, a

.layer of selenium in intimate contact with said nickel layer, a contact layer in intimate contact with said selenium layer, and a contact member engaging said contact layer, said member being of such construction that vapors formed by a lightning discharge puncturing said contact layer can escape freely.

26. A lightning arrester comprising a metal plate, a layer of nickel formed on said plate, a layer of selenium in intimate contact with said nickel layer, a contact layer in intimate contact with said selenium layer, and a mass of metal strands engaging said contact layer.

27. A lightning arrester comprising a metal plate, a layer of nickel formed on both sides of said plate, a layer of selenium in intimate contact with each nickel layer, a thin metal contact layer in intimate contact with each selenium layer, and a contact member pervious to vapors engaging each metal contact layer.

28. A lightning arrester comprising a metal plate, a layer of nickel formed on both sides of said plate, a layer of selenium in intimate contact with each nickel layer, a thin metal contact layer in intimate contact with each selenium layer, and a mass of metal strands in intimate contact with each metal layer. l

29. A lightning arrester comprising an electrode unit consisting of a metal plate, a layer of nickel formed on both sides of said plate, a layer of selenium in intimate contact with each nickel layer, a thin metal contact layer in intimate contact with each nickel layer, a bolt passing through said unit, a mass of metal strands surrounding said bolt and engaging each contact layer, a contact plate engaging the outer side of each mass of metal strands; and means for insulating all of said parts from said bolt.

LARS O. GRONDAHL.

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