US2393584A - Protective device - Google Patents

Description

Jan. 29, 1946.

R. S. BENNETT PROTECTIVE DEVICE Filed May 31, 1943 Inventor: Ralph SBenn "tat, by 6. x7

His A'btovney.

Patented Jan. 29, 1946 UNITED STATES PATENT PROTECTIVE DEVICE New York Application May 31, 1943, Serial No. 489,14?

(c1. IVS-30) 6 Claims.

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 are 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 are extinguishing ability and require high impulse voltages to cause sparkover, thereby impairing the overvoltage protection afiorded 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 efilciency 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 eflicient 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 lssimple in construction, provides better overvoltage protection, is eflicient 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 01' 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 are 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 suflicient 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 eflicient construction,

Referring more particularly to the drawing, I have illustrated a protective device such as a lightning arrester including a tubular member ill of suitable insulating material having disposed therein spaced electrodes ti and 12. The electrodes have ends spaced from each other to provide a, gap space i3, one of the electrodes 1 I being supported through a ferrule It. The electrode H has at the upper end a plate shaped member l5 which is supported on an end iii of the ferrule. A bore ll of the ferrule through which the electrode l l extends is enclosed by a cap l8 which is screwed on the end [6 of the ferrule. The other electrode I2 is supported thro ugh a ferrule l9, and the ferrules are attached to opposite ends of the tube in 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 2| and 22. A vent opening is provided for the arrester illustrated by the plurality of openings 23 in the ferrule l9, the openings providing a vent opening adjacent the electrode [2 which is adapted to be connected to ground. The electrode ll may, of course, be connected 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 l9 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 propert 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 sufilciently large size as to permit expulsion of the are gases caused at least partially byerosion 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 A; 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 1 3' inch with a gap of about 1 inch so as to provide the device with a relativel 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 overthe vent openings 23 for preventing the pellets from passing out the reserve supply of pellets should be left un-'- filled so as to allow for movement of the pellets, and therefore permitting automatic adjustment to the most efficient arc space between pellets during operation after an arc is drawn. Thus the I 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 H and l2. 1 view of improved construction has a relatively high restrike voltage for a. given distance between the electrodes H and I2. 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. I

The pellets it will be seen in the arc chamber provide a variable size are path and furthermore the pellets may be self adjusting, thus giving in efiect 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 l0. 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 am. 'In order to have both a relatively high discharge capacits and stillprevent a conducting path from building up in the interstices between the electrodes with low currents, the air chamber 21 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 3 the electrodes as is described and claimed in the above-mentioned Kalb application.

Although I have shown and described a, particular embodiment of my inventiom'I 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.

of erosion is relatively small as regards the reserve supply-that can be made available, and

thus many additional operation years of life can be provided over that for the ordinary expulsion tube. Operation of my improved circuit interrupting device is as follows: With the electrode H con nected to any suitable source of high voltage, such as a line through: the conventional gap structure, upon a sufilciently high voltage appearing across the electrodes v H and I! an arc will form through the irregular spaces between the interexpel the ionized gases out through i the vent openings 23. If the rate of recovery of the gap space is higher than the rate of rise of the recovery voltage the arc will not restrike in the space What I claim' as new and desire to secure Letters Patent of the United States is:

1. A protective device adapted to interrupt current including at least two electrodes between which an arc can be drawn, a mass comprising essentially spheroidal insulating gas evolving material defining a relatively irregular arc path along the interstices thereof through which the arc may strike between said electrodes, and means. defining avent opening communicating with said are path, saidjspheroidal material being of such size as'to permit expulsion of arc gas through said interstices and to the vent opening communicating with said arc path.

2. A device adapted to interrupt current including a casing providing an arcing chamber, a. pair of electrodes -within said chamber, a. mass comprising essentially pellets of gas evolvable insulating material of spheroidal shape within said chamber defining a relatively irregular arc path through which an arc may strike between said electrodes, and means defining a vent opening through said casing communicating with the arc path, said pellets being of such size as to permit expulsion of arc gas through the interstices between said pellets to said vent opening, a portion of said chamber being left unfilled with pellets so as to allow for movement thereof during operation of the device after an arc is drawn between said electrodes.

3. A lightning arrester including an insulating tubular casing, spaced electrodes within said casing and spaced from the inner walls thereof, a mass within said casing comprising essentially spheroids of gas evolvable insulating material defining an irregular path through which an arc may strike between said electrodes, said mass including spheroids around at least one of said electrodes providing a reserve supply so that any spheroids consumed by discharge may be replenished from the reserve supply.

4. A protective device adapted to repeatedly interrupt current including at least two electrodes between which an arc can be drawn, a mass comprising essentially spheroidal insulating gas evolving material defining a relatively irregular are path along the interstices thereof through which the arc may strike between said electrodes, and means defining a vent opening communicating with the arc path, said spheroidal material being of such size as to permit expulsion of arc gas through said interstices and to the vent opening communicating with the arc path.

5. A protective device adapted to repeatedly interrupt current including at least two electrodes between which an arc can be drawn, a mass comprising essentially spheroidal insulating gas evolving material defining a relatively irreguar arc path through the interstices thereof alon which the arc may strike between said electrodes, and means defining a vent opening communicating with the arc path, said spheroidal material being of such size as to permit expulsion of arc gas through said interstices and to the vent opening communicating with the arc path, and a reserve supply of said spheroidal material so that any such material consumed during subsequent operations may be replenished from the reserve supply. 7

6. A device adapted to interrupt current including at least two electrodes between which an arc can be drawn, a mass comprising essentially spheroids of insulating gas evolving material defining a relatively irregular arc path along the interstices thereof through which the arc may strike between said electrodes, and means defining a vent opening communicating with the arc path, said spheroids being of such size and shape as to prevent packing and thereby retarding of the expulsion of the arc gas through the interstices between said spheroids to said vent opening.

RALPH S. BENNETT.

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