Protective device

Jan. 29, 1946.

2,393,584

R. S. BENNETT

PROTECTIVE DEVICE

Filed May 31, 1943

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Inventor: Ralph S. Bennett, By ⁷ His At/torney.

Patented Jan. 29, 1946

2,393,584

UNITED STATES PATENT OFFICE « 2,393,584

PROTECTIVE DEVICE

Ralph S. Bennett, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York

Application May 31,1943, Serial No. 489,147

Claims. (Cl. 175—30)

My invention relates to protective and circuit interrupting devices, and has application to overvoltage and overcurrent protective devices such as lightning arresters of the type which arcs over to provide a discharge path to drain off lightning surges from the line and then provide an arc extinguishing means to interrupt the flow of overcurrent through the arrester.

Various types of overvoltage protective devices for providing a circuit between an electrical device or line and ground for passage of high voltage impulses have been suggested. One type, referred to as the arc expulsion tube, is provided with spaced electrodes with a surrounding tube of gas evolving material so that when an arc occurs between the electrodes within the tube, gas will be evolved from the tube walls for the purpose of extinguishing the arc caused by the power follow current. In order to extinguish low current arcs such devices are usually made with relatively long gaps so as to provide an arrangement for extinguishing such power follow currents. However, long gaps decrease the high current arc extinguishing ability and require high impulse voltages to cause sparkover, thereby impairing the overvoltage protection afforded by this type of device. Also the gas emitting material of these devices is subject to erosion. The erosion not only tends to weaken the tube, but also reduces the efficiency of the tube for clearing currents of relatively low magnitude so that after a tube has operated several times it may possibly fail at currents in the range within which it was intended to function.

It is an object of my invention to provide an improved protective device or circuit interrupting device which relatively will be more efficient and have a longer life under repeated operation for the range of electrical values for which it was designed to operate.

Another object of my invention is to provide an improved lightning arrester of the expulsion type which is simple in construction, provides better overvoltage protection, is efficient in overall arc extinguishing operation, and which has a relatively long life under repeated operation.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

In the drawing the single figure illustrates a sectional side elevation of a protective device which is provided with an embodiment of my invention.

The construction illustrated in the drawing provides an impulse discharge means for drawing an arc by a pair of electrodes which has a mass of suitable spheroids formed of insulating gas evolving material between the electrodes so as to provide a relatively irregular arc path through the interstices of the spheroids with the interstices of sufficient size and automatically adjustable to permit therebetween the expulsion of the arc gas caused at least partially by the erosion of said material. The spheroids may be formed of any suitable gas evolvable insulating material such as fiber, methyl methacrylate, or cellulose acetobutyrate. The spheroids and electrodes are placed in a tubular member, the electrodes being supported by end caps at the opposite ends of the tubular member. One of the end caps, such as the one supporting the ground electrode is provided with openings so as to provide a venting space communicating with the arc gap. Suitable screen .means may be provided over the venting opening so as to prevent the relatively small fiber pellets from passing out through the vent opening. With this construction there is an intimate association between the arc and the arc extinguishing material or the pellets so as to provide a very efficient construction.

Referring more particularly to the drawing, I have illustrated a protective device such as a lightning arrester including a. tubular member 10 of suitable insulating material having disposed therein spaced electrodes I ί and 12. The electrodes have ends spaced from each other to provide a gap space 13, one of the electrodes 11 being supported through a ferrule 14. The electrode I i has at the uppei· end a plate shaped member (5 which is supported on an end (6 of the ferrule. A bore 17 of the ferrule through which the electrode 11 extends is enclosed by a cap 18 which is screwed on the end IS of the ferrule. The other electrode 12 is supported through a ferrule 19, and the ferrules are attached to opposite ends of the tube 10 in any suitable manner such as by screws 20. An opening is provided in the ferrule 19 and the electrode 12 extends through the opening and is supported on either side of the ferrule by a pair of nuts 21 and 22. A vent opening is provided for the arrester illustrated by the plurality of openings 23 in the ferrule 19, the openings providing a vent opening adjacent the electrode 12 which is adapted to be connected to ground. The electrode 11 may, of course, be con55 ^898,684 nected to a high voltage line through a gap in the conventional manner.

In order to provide an arc extinguishing construction for the protective device the tubular member 10 contains at least in the space between the electrodes a mass of suitable spheroids 25 which are formed of or comprise essentially insulating material having the property of giving off gas when subjected to an arc. The insulating pellets should be of spheroidal shape so that the separate pieces will not provide relatively large adjacent surfaces which will pack and stick to each other after an impulse has passed through the lightning arrester, or during the period when they are subjected to the pressures of the arc gases as would be the case with more finely divided granular material. Furthermore, the insulating spheroids should be of sufficiently large size as to permit expulsion of the arc gases caused at least partially by erosion of the material, without expelling the material as well. A sufficient size of pellets for an ordinary lightning arrester adapted to be operated on about 9 kv. normal voltage is in the vicinity of % inch In diameter. In application, Serial No. 489,149, Kalb, filed concurrently herewith and assigned to the same assignee as this present invention there is described and claimed a protective device employing spheroids within a particular range of between % and A inch with a gap of about 1 inch so as to provide the device with a relatively high restrike voltage. It will therefore be seen that an irregular arc path is provided through the interstices of the material between the electrodes. A suitable screen 26 is provided over the vent openings 23 for preventing the pellets from passing out . through the vent openings 23. It will also be seen that the space between at least one of the electrodes, such as the electrode i ί and the inside walls of the tube 10, is filled with the pellets so as to provide a reserve supply of the fiber pellets. A space indicated by the numeral 27 above the reserve supply of pellets should be left un- filled so as to allow for movement of the pellets, and therefore permitting automatic adjustment ⁴⁵to the most efficient arc space between pellets during operation after an arc is drawn. Thus the interstices between the pellets may be increased a suitable amount depending upon, the volume of gas created when extinguishing low and high currents. As the discharge between the electrodes may consume portions of the fiber pellets the reserve supply will drop down into the gap space so as to maintain a constant condition as long as there is an excess of pellets. The amount between the electrodes ί ί and 12. In view of the relatively long gap space through the circuitous route between the interstices of the pellets my improved construction has a relatively high restrike voltage for a given distance between the electrodes 11 and 12. Thus a relatively small device will provide a relatively high restrike voltage characteristic. Also, in view of the intimate contact between the arc and the various pellets my device has good low current clearage operation as well as high current clearage operation, since the pellets may be placed if desired in a relatively big bore.

The pellets it will be seen in the arc chamber provide a variable size arc path and furthermore the pellets may be self adjusting, thus giving in effect a self adjusting arc chamber and expulsion path. Furthermore, as the pellets are eroded away in the arc path the pellets from the reserve supply can move down and take the place of the eroded ones. Since the discharge capacity of the device is dependent upon the diameter of the arc path and the expulsion path, the larger the diameter the more current may be discharged without bursting the tubular member 10. However, with a relatively small diameter, a sufficiently high velocity of the expulsion gas will obtain so as to permit the extinguishing of low-current discharge Arc. In order to have both a relatively high discharge capacity and still prevent a conducting path from building up in the interstices between the electrodes with low currents, the air chamber 27 provides for automatic expansion of the interstices conforming with the degree of discharge current. Another way of providing a device with a relatively high discharge capacity and still prevent a conducting path from building up in the interstices between the electrodes is to employ a relatively large diameter of arc chamber and provide a relatively restricted passage between the electrodes as is described and claimed in the above-mentioned Kalb application.

Although I have shown and described a particular embodiment of my invention,! do not desire to be limited to the particular embodiment described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.