US2503911A - Protective device - Google Patents

Description

J. v w. KALB PROTECTIVE DEVICE v April 11, 1950 3 Sheets-Sheet 1 FildFeb. 20, 1945 PELLET DIAMETER 25o aoo s50 ENT um E wuwwfl uwwx MQMHRM86420 v SEMUQ v FOLLOW CURR Inventor: John W. Kalb.

. Hi5 Attorney.

April 11 1950 J; W. KALB PROTECTIVE DEVICE a she is-sheet 2 Filed Feb 20, 1945 Ill/III]! fill/Ill) Invehoor: John W. ,Ka|b,

' H is Attorne April 11, 1950 J. w. KALB PROTECTIVE nsvxcs 3 Sheets-Sheet 3 Filed Feb. 20, 1945 w Lama.

I 4 Inventor:

- John W Kalb. v Joy 'flw z/c. JMAH His Attorney.

Patented Apr. 11, 1950 PROTECTIVE DEVICE v John w. Kalb, Pittsfleld, Mass., assignor to Gen: eral Electric Company, a'corporation of New York Application February 20, 1945, Serial No. 578,894

(cans-3o) 8 Claims. 1

My invention relates to protective and circuit interrupting devices and features thereof having application to overvoltage protective devices such as lightning arresters, and to fuse devices, and electric circuit interruptera This application is a continuation-in-part of my application Serial No. 489,149, filed May 31, 1943, now abandoned, and assignedto, the same assignee as the present application.

Various types of overvoltage protective devices for providing a circuit between an electrical device or line and ground for the passage of high 'voltage impulses have been suggested. One type referred to as the expulsion protector 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 an arccaused by the power follow current. There are several incompatible requirements that necessitate a compromise in the design of such expulsion protector tubes. It is desirable that the expulsion protector tube be able to discharge power and impulse currents of large magnitude without bursting, which can be achieved by using a large bore and a short internal gap length within the bore. A short gap length alsogives a low impulse breakdown voltage which is desirable so that the expulsion protector tube can protect insulation against failure. In order to interrupt the power frequency follow current in electrical circuits in which the circuit recovery voltage occurring across the tube at current zero is severe, a long internal gap and a small bore to insure intimate contact between the arc and the gasevolving material are needed. At each operation, the deionizing gas is supplied from material eroded from the side walls of the tube and hence the bore must be made sufficiently small so that this erosion will not enlarge it suificiently to prevent the gap from interrupting the. follow current for a reasonable number of operations. The need for a low impulse breakdown voltage and a large bursting current tend to force the design toward a short gap length and a big bore. However, the necessity of interrupting the follow current and having a long erosion life tends to force the designtoward a long gap length and a small bore. .1

It has been suggested that in order to overcome the eroding of the tube walls that protective devices may be formed with an arc space through which an arc may be drawn between electrodes,

of insulating gas evolvable material, such as fiber pellets, such a construction being described and claimed in patent application Serial No. 489,147, Bennett, filed May 31, 1943, now Patent No. 2,393,584, and assigned to the same assignee as the present application.

It is an object of my invention to provide an improved arc interrupting device having a high impulse and power frequency current discharge capacity, a low impulse breakdown, a long erosion life, and the ability to interrupt follow current in circuits having severe recovery voltage.

A further object of my invention is to provide an improved current interrupting device which is simple in construction, economical to manufacture, and which will have a relatively long life.

It is another object of my invention to provide a new and improved lightning arrester which inthe arc space being filled with a mass of pellets b5 terrupts power follow currents with substantially no emission of flame and with no danger to other equipment or operating personnel. Further objects and advantages of my inven tion will become apparent from the following description referring to the accompanying drawings, 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 this specification.

In the drawings, Fig. 1 is a sectional side elevation of a protective device which is provided with an embodiment of my invention; Figs. 2 and 3 are curve diagrams which will be used in the description of my invention to aid in under-.

standing the same; Fig. 4 is a sectional side elevation of a commercial embodiment of the arrangement disclosed in Fig. 1, and Figs. 5, 6 and 7 illustrate modifications of the device of Fig. 1.

In the arrangements illustrated in the drawings, I have shown my invention as applied to a protective device such as a lightning arrester, but it is to be understood that features of my invention may be adapted for use in any other suitable type of protective or circuit interrupting device. The illustrated construction includes a pair of spaced electrodes within an arc discharge chamber having a massof suitable discrete particles or pieces of insulating gas evolving material so as to provide a relatively irregular arc path through the interstices thereof through which an arc may strike between the electrodes. The particles should be, of suitable size and have a spheroidal shape, so as to prevent packing, and an arrangement may be provided where necessary for changing the volume of the arcing chamber so as to replenish the particles as they are eroded.

Referring to Fig. 1 of the drawing, I have illustrated a protective device including a tubular member Ill suitable insulating material having a pair of spaced electrodes Ii and I2 of suitable conducting material. The electrode H is supported from one end of the tubular member l0 through a member I3 of any suitable material, such as metal, which has a bore it into which one end of the electrode H is threaded. The outer surface of the metallic member l3 has threads so that it may be threaded to the inner walls of the tubular member H) as is illustrated at IS. The outer end of the electrode H may be connected to any suitable high voltage line,

such as the line It, through a conventional external gap H. The other electrode l2 may be supported at the opposite end of the tubular member III through a metallic member l8 which may be threaded into the inner surface of the tubular member as is shown at It. A metallic shoulder may be provided connected to the metallic member I8 which is adapted to be connected to ground through a conductor 2|. The

\ electrode I2 is connected to the metallic member with the construction of Fig. 1 to provide the granular material in the form of pellets of spheroid shape so as to prevent any packing or relatively large voids from being formed in the gap due to the high pressures suddenly formed by impulse. Also the pellets should be of a suitable size, that is within a particular approximate range of diameters as will be described more completely hereinafter with reierence to Fig. 2.

In order to minimize the possibility of coating over a continuous path between the electrodes with a conducting layer of soot, the gas should move with a relatively high velocity. This may be accomplished by using a tube of a relatively small bore as will be described below in relation to Fig. 5. However, the smaller the bore the lower the current discharge capacity. Thus I may employ a tube with a relatively large bore, that 'is about one inch in diameter and with about one 'inch spacing between the electrodes for an arrester designed for operation on a. 7200 volt line, and I provide a restriction in the arc ga between the electrodes by an insulating member 26 which is supported in the side walls 01' the tubular member it between the electrodes so as to define a throatlike arrangement. Thus it will be seen that relatively short axial restricted passage 21 is provided, and the passage or throat 21 is made relatively short so as not to reduce the current discharge capacity of the device.

As an example of proper proportions, the arrester shown in Fig. '1 which is designed to operate on about 7200 volts normal voltage, has a tube internal diameter of one inch and a spacing between the electrodes of one inch, and the restricted passage is about inch in diameter and about it to V inch in axial length. It is to be understood that the above data are given as an M1318 for the constants nf n hnrI-hufln-n aim-ll- 4 and for other operating conditions, of course, the spacings and above data may be varied.

In order to provide a reservoir for extra gas evolvable pellet material it will be seen that reserve pellets are placed adjacent the line electrode II out o! the direct arcing path between the electrodes. As the pellets within the arc space are eroded, the reserve pellets in the space 28 are forced into the arc gap by a resilient means in the form of a spring 29 which expends its stored energy against a suitable plunger 30. Thus it will be seen that the tube walls between the ground electrode 12 and the plunger 30 provides an arcing chamber having a mass of discrete particles of gas evolvable material in the shape of spheroids, and the movable plunger provides an arrangement for varying or decreasing the volume of the chamber so as to replenish the pellets as they are eroded in the arc path. Any other suitable means may be provided for changing the volume of the arcingchamber as the gas evolvable material becomes eroded, and another arrangement will be described below in relation to Fig. 6.

In order to prevent the relatively small spheroids from passing out the vent openings 23 it will be seen that I have provided spheres of graduated size within the space indicated by the numeral 3| which is between the ground electrode and the grating 22. Thus it will be seen that relatively large spheres 32 are provided which rest on the grating 22 and which have a diameter which is substantially the same as the distance between the electrode l2 and the member 18. On top or these spheres 32 I provide relatively smaller spheres which are still, however, larger than the spheroids in the arc space.

In order to prevent the emission of flame from the interrupting device with consequent arc-over toother equipment and danger to operating personnel the electrode i2 terminates at a point considerably removed from the vents 23 and as was mentioned above the intervening space is filled with pellets. By making this space between the arcing end of electrode I2 and the vents 23 sufilciently long as illustrated, the hot arc gases are sufficiently cooled before expulsion to atmosphere so that no flame is expelled.

In order to provide strength and to reduce impulse breakdown voltage the tubular member in in the vicinity of the arcing chamber between electrodes H and I2 is surrounded by a grounded lmetalI sleeve 33 closely embracing tubular mem- Operation of my improved protective device is as follows: When a high voltage surge strikes the line it and breaks down the series gap ll, an arc will form between the electrodes H and I2 in the circuitous path defined by the interstices between the fiber pellets. Since the pellets are made of any suitable insulating material which produces deionizing gas when subjected to an arc, gas will be produced while current flows, and these gases escape through the vent openings 23. As the follow current passes through zero.

these gases between the electrodes H and I2 cool and demobilize the residual ions in the arc space, and cause rapid build-up of recovered dielectric strength of the gap. Then, if the recovered di electric strength or the gap is greater than the transient circuit recovery voltage applied to the gap, the gap will not continue to carry current and the arc is interrupted.

I have found from tests in alternating current in recovered dielectric strength of e gap is a function of the size of the pell and thus the smaller the pellets the higher the recovered dielectric strength. This is illustrated in Fig. 2 in which restrike voltage in crest kilovolts per inch of gap length is plotted on the ordinate axis and pellet diameter is plotted on the abscissa axis. It will be seen that the curve approximates a rectangular hyp'erbola for pellet diameters of 1 inchv to inch. This indicates that the restrike voltage is inversely proportional to pellet diameter in this size range. 1

It is'within the contemplation of my invention to use pellets smaller than 6 inch diameters. However, pellets of 3 inch diameter give suiflaaoacu I 6 material, tests were made over the entire current range to determine the practicability of the principle and to determine quantitatively the ciently high restripe voltage to make unnecessary the use of smaller pellets that are more'expensive and diflicult to manufacture. If a restrike voltage t as high as to kilovolts per inch is not required, it-,will be seen from the curve that larger pellets may be employed. Smaller pellets evolve more gas, and they offer more restriction to the amount of reserve materialneeded. Thus when inch diameter pellets were employed in a device, as shown in Fig. 1, and havinga one inch spacing between electrodes with the amount of pellets in reserve about equal to the amount between the electrodes, the device had an erosion life very much greater than can be obtained with the conventional expulsion tube with cylindrical bore.

Another advantage of the large arc chamber has reached the tube wall it has been attenuated the arrester is able to limit the applied voltage tests made to determine the minimum restriking voltage to be plotted in Fig. 2. In Fig. 3 I have illustrated the effect of the follow current magnitude on restrike voltage for 1*; inch diameter pellets, and in Fig. 3 the restrike voltage in crest kilovolts per inch of gap length is plotted along the ordinate axis while the 60 cycle follow current in crest amperes is plotted on the abscissa axis. This curve has a definite minimum point believed to be due to the different mechanism of arc deionization at different follow currents. At low currents little gas is evolved and deionization is principally due to cooling the arc gases by contact with the pellet surfaces. As the current is raised 'causing more heat, cooling and the resultant deionization will occur at a lower rate with consequent reduction in restrike voltage. However, if the follow current is raised still more causing enough heat to evolve large qantities of gas, deionization occurs at a higher rate due to the injection of this gas into the arc path. It is this phenomenon which apparently causes increase in the restrike voltage after the follow current is increased beyond about 60 crest amperes for 1 6 inch diameter fiber pellets.

Test results such as shown in Figures 2 and 3 indicate that a protective device formed according to my invention with the electrodes spaced, for example one inch, can withstand a circuit recovery voltage of 20 kv. crest which could be obtainedjn a conventional expulsion protector tube only with a gap length of the order of two inches.

Since one of the important features of my improved device is renewability of gas evolvable by'the passage between the pellets thus relieving the impact force on the tube itself. This effect is made certain since the restriction centers the discharge in the tube. p

In Fi 4 I have illustrated a commercial embodiment of the protective device of Fig. 1. The similarity between the two constructions is obvious. A tubular insulating member 34 surrounded by a weatherproof insulating member 35 contains a pair of spaced electrodes 36 and 31.

A metal plug 38 having a central opening 33 is threadedly mounted within the upper end of tubular member 34 with a flanged portion 40 extending outside tubular member 34. Electrode 36 is provided with a Washer 4| .which engages the upper end of the electrode 36 and a recess in the upper end of plug 38 when electrode 36 is inserted in opening 39, as shown in Fig. 4. A metal cap 42 clamps the washer 4| engaging electrode 36 between a lock washer and plug 38 as it threadedly engages fiange 40. A stud 43 threadedly engaging cap 42 holds one terminal 44 of gap I! in position and also holdsan insulating 1cap45 for weather protection purposes in posiion.

The lower end of concentric tubes 34 and 35 are enclosed within a, metal reinforcing sleeve 45 which is held in position by a flanged plug 46 supporting lower electrode 31 as indicated at 41, and provided with vents 48. A suitable gas deflector 49 is threadably mounted tofiangedplug 46. The vents 48 and electrode 31 are arranged with respect to large graduated pellets so as in Fig. 1, to eliminate or suppress flame emission.

An insulating member 5| threadably mounted within tubular member 34 between electrodes 36 and 31 defines a restricted section or throat portion below the reserve pellet column 52. As in Fig. 1 a spring 53 having one end engaging with a plunger 54 and the other end engaging plug 38 is provided to change the volume of the. arcing chamber as erosion of the pellets occurs.

Tests were made over a range of follow cur- 7 inch ininternal diameter of .16, %or 56 inch no trouble occurred and an examination of the arc chamber showed that the pellets had im ufllclent sooting to interfere with follow current interruptions. It will be understood, however, that'the smaller dlameter'arc chambers while being freer from sooting burst at lower values of discharge tion operated satisfactorilywithout any restricted passage. The device includes a pair of electrodes 55 and 8 inside a tubular member 51. A suitable plunger 58 is provided which is biased but spring it so as to change the volume of the arcing chamber and thereby maintain a supply of Dellets between the electrodes, this latter feature being similar to that shown in Figs. 1 and 4. It should'be noted that plunger 58 is indicated as formed of insulatlngqnaterial as contrasted with the metal plungers 30 and 54 of Figs. 1 and 4, respectively.

In Fig. 6 I have illustrated a lightning arrester having ,a pair of electrodes ill and 6| mounted within an insulating tube 62, the structure illustrating a modified arrangement for obtaining a variable volume of the arc chamber as the dis-' crete particles or pieces of are extinguishing material are eroded. The construction illustrated includes a member 63 having the line electrode 60 supported therefrom. The grounded electrode Si is supported through member 64. In order to provide an arcing chamber the volume of which is variable, the arcing chamber is formed by a tubular.member 65 which is made of any suitable resilient material such as rubber. The member i is filled with a suitable arc extinguishing material such as fiber scrap or lathe turnings 66. The upper end of the chamber is sealed by a member '61 which is placed inside one end of the rubber tube 65. A clamping ring 68 tightly holds the tubular member 65 around the member 61. The lower end of the tubular member 65 is tightly supported around a member 69 by another clamping band 10. Suitable vent openings H are provided in the member 69. It will therefore be seen that as the fiber turnings 65 are eroded due to arcing between the electrodes the resilient material which has been extended or expanded in its shape so as to be filled with the fiber scrap will begin to contract thus maintaining the space between the electrodes filled with the fiber lathe turnings. It was found that with the construction as is shown in Figs. 1, 4 and 5 having axially movable plungers 30, 54 or 58 that it is necessary with that construction to employ spheroidal shaped members for good practical results. However, when discrete particles in the form of lathe tumings are employed a radially contractable construction as is shown in Fig. 6 may be employed. It-should be noted that the electrode Bl extends within the arc extinguishing material 66 and if it is made to extend a sufiicient distance and with the vent ll arranged as shown, no flame will be emitted from the vent.

Force is necessary to maintain the pellets in contact in the space between the electrodes when the follow current approaches zero and immediately afterward in order for the arrester to interrupt the follow current. At this instant there 75 I aeoacii I may be men pellets in can 8M, either. because the total volume of pellets in the are chamber-has been greatly reduced by erosion. or

becauseon each operation of the arrester. as the discharge current and pressure increase, the pellets will be blown from the space between the electrodes into any free volume that may exist in the arc chamber, either above or below this space. In order to interrupt the follow current, the pellets must be returned and maintained in contact in the space between the electrodes, by the time the power follow current approaches the first zero. Mechanical means can be used to compensate for erosion and return the pellets to the are space after each operation and such means are shown in Figs. 1, 4,5 and 6. However, it is advantageous to make use of the gas pressure for, this purpose,

which can be done if the arc chamber has suitable proportions such as is shown in Fig. 7. In this construction the pellet column is sufllciently long so that even when operated at low currents, enough gas is developed to insure a high pressure differential between the closed and vented ends of the pellet column so that when the current and the pressure decrease from the maximum value toward zero, the whole pellet column is forced from the closed end toward the vent even though no spring is used. This pressure maintains a compact mass of pellets near the vent end of the arrester as the follow current approaches zero and thus fulfills the conditions essential for follow current interruption until the column of pellets in the arc chamber has been reduced by the erosion resulting from many operations to such an amount that its restored dielectric strength is insuiilcient.

In Fig. 7 I have illustrated a modification of my invention in which no restriction is provided in the pellet column, as in Figs. 1 and 4, and in which no spring and plunger is required.- The arrangement in Fig. 7 comprises a long are gap a tube of insulating material 12 having the lower portion thereof enclosed within a grounded metal sleeve 13. The upper portion thereof is preferably enclosed in an insulating sleeve 14 which is weather resistant. Reinforcing grounded metal sleeve 13 is held in position by a flanged plug 8| threadedly mounted in the lower end of tube 12. This flanged plug is provided with vents 15. The

end of flanged plug 8! extending into tubular member 12 provides the lower electrode which is removed sufliciently from the vent 15 to enable the flame suppression arrangement described above to be employed. As in the preceding constructions, large pellets of graduated size 16 are placed adjacent the vent 15 below the arcing surface of the lower electrode whereby the gases expelled from the pellet column 11 are cooled in flowing through the network of supporting pellets whereby the amount of flame is reduced.

The upper end of tubular 'member 12 is closed by a metal plug 18 to which is threadedly mounted the upper electrode 19 which is suitably connected to the external gap i! as indicated. Preferably a cap is provided to close and protect against the weather the upper end of the protective device.

I have found that by increasing the length of the arc in the column of pellets more gas is proasospu current to 1500 crest amperes on an 8250 volt such an arrester would limit the 60-cyc1e follow circuit having a fault current of 3400 R. M.- S.

amperes. This is a' limitation of follow current to about of theavailable circuit current. It will be observed that with this construction very desirable current limiting action is obtained.

Breakdown voltage of the relatively long gap between electrodes 8| and I9 is held down to reasonable values by virtue of the grounded metal sleeve 13. This'tends to maintain the inner wall of the arc chamber at ground potential resulting in the formation of streamers from the top electrodes 19 with progressive breakdown of the entire gap at relatively low voltage, as will be obvious to those skilled in the art. As in the arrangement disclosed in Fig. 5 the diameter of the arc chamber is small enough to make unnecessary the use of a restricted passage. Also the gap length is so long that the recovered dielectric strength per inch of pellet column can be made much lower than in the arrangements described above. Also the large volume of gas produced by virtue of the long are provides a large pressure differential between the top end of the column and the vented end which will pack the pellets toward the vented said electrodes, and means defining a restricted portion between said electrodes so that gas may be forced through a restricted area between said electrodes at a relatively high velocity so as to minimize sooting over any continuous path be- I tween the electrodes.

4. A device adapted to interrupt current including a pair of electrodes, a mass of spheroids of gas evolvable insulating material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, said spheroids having an approximate diameter of within'the range of about to r; of

end, whereupon the spring and plunger arrange- I Letters Patent of the United States is:

1. A device adapted to interrupt current including a pair of electrodes, a mass of granular insulating gas evolvable material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, and means defining a restricted portion between said electrodes so as to force gas through a restricted area between said electrodes at a relatively high velocity.

2. A device adapted to interrupt current including a pair of electrodes, a mass of granular insulating gas evolvable material defining a relatively irregular arc path'through the interstices thereof through which an arc may strike between said electrodes, an insulating casing around said electrodes and said mass, means defining a vent opening through said casing and communicating with the arc path, and insulating means extending from. the inner surface of said casing between said electrodes providing a restricted portion in the arc path between said electrodes.

3. A device adapted to interrupt current including a pair of electrodes, a mass of pellets of gas evolvable insulating material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between from.

, casing communicating with the arc path adjacent an inch so as to provide a relatively high restrike 18' voltage in volts per inch of gap length. and insulating means defining a restricted portion between sald electrodes so as to force gas through a restricted area between said electrodes at a.

' relatively high velocity.

5. A device adapted to interrupt current in-' cluding-a pair of electrodes, 9. mass of spheroids of gas evolvable insulating material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, said spheroids having an approximate diameter within the range of about to 1 of an inch so as to provide a relatively high restrike voltage, an insulating casing around said electrodes and said mass of spheroids, means defining a vent opening through said casing and communicating with the arc path, and insulating means defining a restricted portion between said electrodes so that gas may be forced through a restricted area between said electrodes.

6. A device adapted to interrupt current in- I cluding a pair of electrodes, a mass of spheroids of gas evolvable insulating material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, said spheroids having an approximate diameter of within the range of about o x; of an inch sons to provide a relatively high restrike voltage, an insulating casing around said electrodes and said mass of spheroids,

means defining a vent opening through said casing and communicating with the arc path adjacent one of said electrodes, and insulating means defining a restricted portion between said electrodes so that gas may be forced through a restricted area between said electrodes.

'7. A device adapted to interrupt current including an insulating casing, spaced electrodes within said casing and spaced from the inner walls thereof, a mass of granular insulating material of gas evolvable material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, said mass including granules around at least one of said electrodes providing a reserve supply, resilient means for forcing said reserve supply into the space between said electrodes, insulating means defining a restricted portion between said electrodes so that gas may be forced through a restrictedarea between said electrodes, and means providing a vent opening through said one of said electrodes.

, 8. A device adapted to interrupt current including an insulating tubular casing, spaced electrodes within said casing and spaced from the inner walls thereof, a mass of spheroids of gas evolvable insulating material defining a relatively irregular arc path through the interstices thereof through which an arc may strike between said electrodes, said mass including spheroids around inch,- resilient means for forcing said reserve supply into the space between said electrodes, in- I sulating means defining a restricted portion between said electrodes so that gas may be forced through a restricted area between said electrodes, and means providing a vent opening through said casing communicating with the arc path adiacent one oi'said electrodes.

JOHN W. KALB.

"12 REFERENCES CITED The following references are of record in the tile of this patent:

UNITED sums P A'I'ENTS 1 Date Number Name 501,241 Browne July 11, 1893 2,290,639 Evans July 21, 1942 2,393,584 Bennett Jan. 29, 1946 FOREIGN PATENTS Number Country Date Great Britain Mar. 4, 1942

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