US2546006A - Lightning arrester - Google Patents

Description

March 20, 1951 M. G. LEONARD ET AL LIGHTNING ARRESTER Filed Nov. 28, 1947 H 7 a M n 3 0 a 3. 2 m x M n m4 I n m 5 .m M F a x m w E w .m M 4 b G a. a m MW H w m L I I Z H 1 0 1 A v 1 /H/////H//// ////////H////////H/////H/ 5 I r I 0 U I H j s o 5 1 1 2 s z 3 a F & Z w ///W 4 9 a s .L). w. q. B s n m 2 f m Guy XI /aye BY fl% ATTO EY "rupting characteristics, but which -means for relieving the gas pressure, so that excessive pressures do not occur, and the necessity for unduly great mechanical strength or the use of a series resistor is eliminated.

' A further object'of the invention is to provide 'a lightning 'arrester of the expulsion type in which a loose stack of flat, circular elements is disposed between the electrodes to restrict the are path, the circular elements being free to Patented Mar. 20, 1951 UNITED STATES PATENT OFFICE Sharpsville, -Pa.,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 28, 1947, Serial No. 788,370

9 Claims. 1 The present invention relates to excess voltage protective devices, or lightning arresters, and more particularly to an improved lightning arrester of the expulsion type.

Expulsion lightning arresters consist essentially of spaced electrodes extending into a chamber, usually a cylindrical tube, which is lined with or contains material, such as hard fibre, which is capable of evolving gas when heated by an electric arc, one of the electrodes being vented to permit escape "of the gas generated during operation. When a voltage surge is discharged, an arc is formed between the electrodes. and large quantities of un-ionized gas are evolved which mixes turbulently with the arc gases, and the arc is blown out, and the arc path deionized, by the blast of gas, which escapes through the vent, thus interrupting the power current which tends to follow a discharge, usually within the first half-cycle. In order to obtain good interrupting characteristics, especially for low currents, the arc path must be relatively constricted, and it is customary to design expulsion lightning arresters with means for restricting the arc path so that the arc occurs in a relatively narrow space. When high power currents occur, however, the large quantity of gas produced in a very brief time in the restricted space results in extremely high gas pressures, causing severe impact stresses, or explosive forces, on the tube. In order to Withstand these severe bursting forces, the tube'm'ust be designed to have very high mechanical strength; and it has frequently been necessary to use a resistor in series with lightning arresters of this type 'inorder to limit the power current to a safe value.

It is a principal object of the present-invention to provide a lightning arrester of the expulsioi'i type which has good interrupting characteristics rcr both high and low power currents, but in which the development "of excessive gas pressures is prevented.

Another object of the invention is to provide a lightning arrester of the expulsion type in which the arc path is restricted to provide good "interincludes move axially to permit gas to flow between them during a discharge, and some of the elements preferably having a central space into which .gas may flow to relieve the gas pressure without materially affecting the restriction of the arc path. Preferably, also, additional gas storage space is provided in the unvented electrode to 'furtherassist in keeping down the gas pressure.

Other objects and advantages of the inven t-ion will be apparent from the following detailed description, taken in-connection with the accompanying drawing, in which:

Figure l is a vertical sectional view of an expulsion lightning .arreste'r embodying the invenl tion;

.Figs, 2 and 3 areperspective viewsof elements of the arrester of Fig. .1;

Fig. 4 is a fragmentary vertical sectional view of a lightning arrester showing a modified embodiment of the invention;

:Fig. 5 is a perspective View of a Washer element utilized in the embodiment 'of Fig. 4;

Fig.6 is a'perspective View showing an alternative form of washer element which may be used in the embodimentof Fig. 4;

Fig. '7 is a fragmentary vertical'sectional View of another embodiment of the invention; and

Figs. 8 and 9 are perspective views ofel'ement's of the lightning 'arrester assembly of Fig. 7.

A preferred embodiment of the invention is shown in Fig. 1. The lightning arrester shown in this figure includes a cylindrical tube I of hard fibre, or:other suitable insulating material which :is capable of evolving :gasin the presence of an electric arc, and which has sufiicient mechanical strength. The tube 1 is shown as a single piece of tubing, but it will be understood that any suitable tubular structure may be used having a cylindrical internal surface 'of insulating, gasevolving material. Ihe tube l is internally threaded at each end for the reception of op;- posed, spaced electrodes. An upper electrode member -2 is threaded in the upper end of the tube I, and in the particular embodiment illustrated, consists of "a tubular metal member terminating in a fiat electrode portion or head '3 of smaller diameter. The electrode member 2 has a plurality of openings '4 around the'electrode .3 to provide communication between the tube 1 and the interior of the hollow electrodermember 2. A cap'member 5 is threaded on the upper end of the upper electrode member 2rand engagesthe upper end of the tube 1 to close the top of the assembly with a substantially Egas tight :joint. A terminal stud S is threaded into the 'cap to 3 provide electrical connection to the upper electrode.

The lower electrode member I is a hollow, tubular metal member which is threaded into the lower end of the tube I, and which has an electrode portion or head 8 similar to the electrode portion 3 of the upper electrode. A plurality of vent openings 9 is provided around the head 8 to permit escape of gas from the interior of the tube 1 through the hollow lower electrode member 1. The electrode portions 3 and 8 of the upper and lower electrode members 2 and l are spaced apart within the tube I, the distance being determined by the desired break-down voltage of the tube, and the arrangement is such that the arcing distance between the electrodes within the tube is considerably less than the spark-over distance on the outside of the tube, so that discharges between the electrodes always occur within the tube.

A loose stack of flat, circular elements is disposed within the tube in the space between the electrodes. In the preferred embodiment shown in Fig. 1, this stack consists of a plurality of alternate rings or washers 5E] and discs H. The washers Ii] are made of hard fibre, or other suitable insulating, gas-evolving material, and while they may be punched from sheets, they are preferably cut from fibre tubes because of the greater strength and toughness due to the circumferential grain structure. Each of the washers it has a relatively large central space and has a slot l2 cut through it, the sides of the slot being spaced apart so that the washer is radially compressible by closing the slot [2. The slot I2 is preferably disposed at an angle to the axis of the washer, as shown in Fig. 2, to

increase the compressibility by allowing the sides of the slot to slide on each other. The discs H are imperforate discs of hard fibre, or other insulating, gas-evolving material, and each disc has a plurality of radial grooves 13 formed in at least one of its surfaces. In the preferred structure, as shown in Figs. 1 and 3, each disc has four grooves 13 in each surface, the grooves on opposite sides being staggered, to avoid undue weakening of the disc, and decreasing in depth toward the center of the disc. The top and bottom discs of the stack may have grooves upon one side only as shown in Fig. 1.

The washers are of such a diameter that they fit closely in the tube I with a slight radial clearance between the washers and the tube to provide a restricted arc path. The discs H are made of somewhat smaller diameter to increase the turbulence of the gas evolved in operation. The discs and washers are alternated with each other and are disposedin a stack which is of less height than the distance between the electrodes 3 and 8, so that under normal conditions there is a space between the top of the stack of discs and washers and the upper electrode 3, as shown in Fig. 1. The discs and washers are stacked loosely so that they are free to separate and move axially in the tube l, and the washers are disposed so that the slots l2 are not in'alignment in order to avoid establishing a relatively unrestricted path for a discharge. The angular disposition of the slots l2 has the efiect of lengthening the arc path, however, if a discharge happens to strike through one or more of the slots, and this effect is especially important in case the slots are inadvertently aligned. The arrester assembly proper, including the tube I with its associated electrodes, is preferably enclosed in a porcelain housing I4 which may rest on a perforated washer l5 clamped between a shoulder on the lower electrode member l and the lower end of the tube 1. A gasket I6 is preferably placed between the housing [4 and the washer 15. A metal cap member ll closes the top of the porcelain housing [4, a gasket l8 being interposed between the cap I! and housing 14, and the cap ll is engaged by a flange portion I9 on the terminal stud 6. A packing gasket 28 is placed between the flange I9 and the cap H, and it will be seen that when the terminal stud 6 is tightly screwed down, the entire assembly is rigidly held together. A suitable nut and washer 2 i, or other terminal means, may be provided on the stud 6 for securing a line lead to the stud. The lower electrode member l is threaded into a supporting plate or bracket 22 and held in place by a lock washer 23. If necessary or desired, a deflector member 24 may be secured to the supporting plate 22 in order to direct the blast of gas discharged from the lower electrode member I in a desired direction away from adjacent conducting parts.

In use, the terminal stud 6 is connected to a terminal of a transformer, or other protected apparatus, or to a line conductor 25, through an external series spark gap 26 which may take any suitable physical form. The lower electrode member I is grounded through the supporting plate 22, as indicated at 21. Under normal conditions, the series gap 26 isolates the arrester from the line voltage so that the fibre tube I will not be continuously subjected to this voltage. Upon the occurrence of a lightning surge, or other excess-voltage surge, which exceeds the break-down voltage of the arrester, the external gap 26 and the internal gap between the electrodes 3 and 8 break down to discharge the surge to ground. An arc is thus established between the electrodes 3 and 8 in the restricted path between the washers i0 and the wall of the tube i, the imperforate discs ll preventing a discharge through the central spaces of the washers Ill. As soon as the arc strikes between the electrodes 3 and 8, a large quantity of relatively un-ionized gas is evolved from the fibre tube l and the fibre washers Ill and discs II. This gas mixes turbulently with the arc gases and is discharged in a blast through the vent openings 9 and tubular lower electrode member I, thus blowing out the arc and deionizing the arc path, so that the arc is extinguished and the power current interrupted.

When the current is relatively large, very large quantities of gas are evolved in the restricted arc space in a very brief time, 50 that the gas must be discharged through the vent openings 9 rapidly enough to prevent the development of very high pressures. The gas in the arc path, however, flows through the grooves I3 in the discs ll into the central spaces of the washers H which provide additional space for the gas and thus relieve the pressure. The gas flowing in this way between the discs and washers tends to blow them apart axially, raising the uppermost disc against the top electrode 3, and separating the other discs in the stack, thus making available more space for the gas and further reducing the gas pressure. The gas at the upper end of the arc path also flows through the openings 4 into the interior of the hollow upper electrode member 2, which provides additional gas storage space and further relieves the pressure. If the gas pressure in the arc path is sufliciently high,

streets the washersfto will be radially compr ssed y closing the slots I2, thus enlargin'g the arc path and reducing the gas pressure. If the pressure is extremely high, the sides of the slots I2 may slide on each other to further compress the wa h; 'rs'. When the washers are compressed in this way, the area of the arc path is, of course, in creased, but since substantial compression of the washers occur only under very high gas pressures, that is under conditions of very heavy currents, the interrupting ability of the arrester is not seriously affected. When the washers are compressed, their resilience tends to restore them to' their normal size so that a force' is continuously exerted tending to reduce the area of the arc path, which further improves the interruptability or thearrester. This effect has another advantage in that the washers can be som pressed to "permit the passage of very high surge currents but immediately return to their normal size for effective interruption of low power-follow currents. I

The construction described provides considerable gas storage space within the lightning arrester in the central spaces of the washers I0 and in the hollow upper electrode member 2, s6 that the gas evolved in the restricted arc path can flow into these spaces and the gas pressure is relieved. Since the washers II) are not substantially compressed, except when very high gas pressures tend to occur, the restriction of the arc path is maintained, and thus the arrester has excellent power current interrupting characteristics for both high and low currents, but the development of excessive gas pressures is prevented.

It will be apparent that various modifications of the preferred embodiment just described may be made within the scope of the invention. Thus, the gas storage space provided in the upper electrode may not always be necessary and this electrode may, in some cases, be made solid. In some instances, where gas storage space is provided in the upper electrode, it may not be necessary to provide gas storage space in the stack of circular elements, and the washers I0 may be replaced by solid discs, resulting in a stack of discs of alternately large and small diameter. The operation and effectiveness of such a modification will obviously be similar to that of the structure described above.

Another alternative construction is shown in Figs. 4 and 5. Fig: 4 shows a fragmentary view of a portion of the fibre tube I of a lightning arrester similar to that shown in Fig; 1. In this modification, the stack of circular elements consists of alternate imperforate fibre discs 30 and fibre washers 3|, but the discs 39 and washers 3| are all of the same diameter, fitting in the tube I with a small radial clearance and the washers 3I, as shown in Fig. 5, are not slotted so that they are not significantly compressible. If desired, the discs 30 could be made ofsmaller diameter than the washers 3 I in order to increase the turbulence of the gas. In this embodiment of the invention, radial grooves 32 are provided in one surface of each of the washers 3I to allow gas to flow into the central spaces of the washers. The discs an and washers 3I are assembled in a loose stack in the tube I in the same manner as the discs and washers of Fig. 1, and it will be apparent that the operation of this embodiment of the invention is similar to that described above. That is, when an arc occurs in the restricted space between the stack of discs 6 and washers and the we-i1- oi the tube I, the gas evolved in the restricted arc path flows through the grooves 32 into the central spaces of the washers 3| to relieve the pressure and to force the discs and washers apart to further reduce the gas pressure.

Fig. 6 shows an alternative form of Washer 33 which may be used in the assembly of Fig. 4. The washer 33 is similar to the washer 35 except that it has a. plurality of shallow radial grooves or de pressions 34 formed in both surfaces. The grooves 34 can readily be formed by pressing them in the washer so that the washer 33 can be produced more cheaply than the washer 3i, in which the grooves 32 have to be cut in a separate operation. The washer is assembled with the discs 3E1 in the manner shown in Fig. 4, and the operation of the assembly is the same as previously described.

Fig. 7 shows a still iurther modification of the invention in which washers 35 and discs 36, shown in Figs. 8 and 9, are utilized. In this embodiment, the washers 35 and the discs 36 are of the same diameter, and both washers and discs have radially extending fingers or lugs 37. The washers 35 and discs 36 are assembled alternately in a loose stack in the fibre tube I, as shown in Fig. 7, similarly to the stack of Fig. 1. The extending lugs 37 space the washers 35 and discs 36 from the wall of the tube I, and center them in the tube, leaving a narrow radial clearance for the arc path between the stack of discs and washers and the tube I. In assembling the stack, the lugs 37 of adjacent elements are staggered; as shown in Fig. 7, so as to permit free axial how of gas. The washers 35 have radial grooves 323 in one surface to permit the gas to how into the central spaces of the Washers, as in the previously described embodiments of the invention. It will be apparent that the operation oi the assembly of Fig. 7 is the same as that previously described. This ar rangement has the advantage, however, that the lugs 31 positively hold the washers 35 and discs 36 centered in the tube I, so that these elements cannot move sideways under high gas pressure, and thus the restriction of the arc path is maintained and it is not increased in area during a discharge, which may occur in the other embodiments of the invention where the washers and discs may be forced sideways against the opposite side of the tube i.

It should now be apparent that an expulsion lightning arrestei' has been provided which has very good current interrupting characteristics, for both low and high currents, but in which the development of excessive gas pressures i prevented because of the provision made for the relief of the gas pressure by permitting gas to flow into storage spaces within the arrester. The loose stack of fiat, circular elements between the electrodes provides a restricted arc path, so as to insure the desired interrupting ability, but permits relief of gas pressure so as to prevent the development of dangerously high pressures with resultant risk of bursting the arrester. Certain preferred embodiments of the invention have been shown and described for the purpose of illustration, but it will be apparent that various other embodiments and modifications may be made within the scope of the invention; and it is to be understood, therefore, that the invention is not limited to the specific arrangement shown, but in its broadest aspects it includes all equivalent modifications and embodiments which come within the scope of the appended claims.

We claim as our invention:

1. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presence of an electric are, a pair of metal electrodes extending into opposite ends of said tubular structure, one of said electrodes being vented, a plurality of imperforate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and Washers being disposed alternately in a loose stack in the tubular member between the electrodes, and the height of the stack of discs and washers being less than the distance between the electrodes to permit the discs and washers to move axially in the tubular structure.

2. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presenc of an electric arc, a pair of metal electrodes extending into opposite ends of said tubular structure, one of said electrodes being vented, a plurality of imperfcrate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and washers being disposed alternately in a loose stack in the tubular member between the electrodes, alternate ones of said discs and washers having radial grooves in at least one surface thereof, and the height of the stack of discs and washers being less than the distance between the electrodes to permit the discs and washer to move axially in the tubular structure.

3. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presence of an electric arc, a pair of meta-l electrodes extending into opposite ends of said tubular structure, one of said elec trodes being vented, a plurality of imperforate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolv ing gas in the presence of an electric arc, the discs and Washers being disposed alternately in a loose stack in the tubular member between the electrodes, the washers being of. larger diameter than the discs and being discontinuous so as to be radially compressible, each of the discs having radial grooves in at least one surface thereof, and the height of the stack of discs and washer being less than the distance between the electrodes to permit the discs and washers to move axially in the tubular structure.

4. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presence of an electric arc, a pair of metal electrodes extending into opposite ends of said tubular structure, one of said electrodes being vented, a plurality of imperforate disc and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and washers being disposed alternately in a loose stack in the tubular member between the electrodes, the washers being of larger diameter than the discs and each Washer having a slot therethrough extending at an angle to the axis of the washer, the sides of the slot being spaced apart so that the washer is radially compressible, each of the discs having radial grooves in at least one surface thereof, and the height of the stack of discs and washers being less than the distance between the electrodes to permit the discs and washers to move axially in the tubular structure.

5. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presence of an electric arc, a pair of metal electrode extending into opposite ends of said tubular structure, one of said electrodes being vented, and the other of said electrodes having a hollow therein communicating with the interior of the tubular structure, a plurality of imperforate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and washers being disposed alternately in a loose stack in the tubular member between the electrodes, the washers being of larger diameter than the discs and fitting in the tubular structure with a small radial clearance, the washers being discontinuous so as to be radially compressible and each of the discs having radial grooves in at least one surface thereof, and the height of the stack of discs and Washers being less than the distance between the electrodes to permit the discs and washers to move axially in the tubular structure.

6. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the presence of an electric arc, a pair of metal electrodes extending into opposite ends of said tubular structure, one of said electrodes being vented, a plurality of imperforate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and washers being disposed alternately in a loose stack in the tubular member between the electrodes, said discs and washers having means for centering them in the tubular structure and for spacing them from the Wall of the tubular structure, alternate ones of said discs and washers having radial grooves in at least one surface thereof, and the height of the stack of discs and washers being less than the distance between the electrodes to permit the discs and washers to move axially in the tubular structure.

'7 An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of material capable of evolving gas in the Presence of an electric are, a pair of metal electrodes extending into opposite ends of said tubular structure, one of said electrodes being vented, a plurality of imperforate discs and a plurality of annular washers in the tubular structure, said discs and washers being made of an insulating material capable of evolving gas in the presence of an electric arc, the discs and washers being disposed alternately in a loose stack in the tubular member between the electrodes, said discs and washer having radially projecting lugs thereon for centering them in the tubular structure and for spacing them from the wall of the tubular structure, the washers havin radial grooves in at least one surface thereof, and the height of. the stack of discs and washers bein less than the distance between the electrodes'to 9 permit the discs and washers to move axially in the tubular structure.

8. An excess voltage protective device comprising a tubular insulating structure having a cylindrical interna1 surface of insulating material capable of evolving gas in the presence of an electric are, a pair of metal electrodes disposed at opposite ends of the tubular structure, at least one of said electrodes extending into the tubular structure, and at least one of the electrodes being vented, and a plurality of flat circular elements of insulating material which is capable of evolving gas in the presence of an electric are, at least some of said circular elements being imperforate, the circular elements being disposed in a loose stack free of axial restraint in the tubular structure between the electrodes to define an axially extending arc path between the peripheries of the circular elements and the internal surface of the tubular structure, at least some of said elements being constructed to provide space for expansion of evolved gases upon separation of said elements by gas pressure, and the height of the stack being less than the distance between the electrodes to permit the circular elements to move apart freely in the tubular structure.

9. An excess voltage protective device comprising a tubular insulating structure having a cylindrical internal surface of insulating material capable of evolving gas in the presence of an electric arc, a pair of metal electrodes disposed at opposite ends of the tubular structure, at least one of said electrodes extending into the tubular structure, and at least one of the electrodes bein vented, and a plurality of flat circular elements of insulating material which is capable of evolving gas in the presence of an electric arc, at least some of said circular elements being imperforate, the circular elements being disposed in a loose stack free of axial restraint in the tubular structure between the electrodes to define an axially extending arc path between the peripheries of the circular elements arid the internal surface of the tubular structure, alternate ones of the circular elements being of larger diameter than the intervening ones, at least some of said elements being constructed to provide space for expansion of evolved gases upon separation of said elements by gas pressure, and the height of the stack being less than the distance between the electrodes to permit the circular elements to move apart freely in the tubular structure.

MERRILL G. LEONARD. GUY Y. HAGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,065,802 Graves Dec. 29, 1936 2,147,440 Hodnette Feb. 14, 1939 2,231,576 Grosse Feb. 11, 1941 2,338,479 Ackermann Jan. 4, 1944 2,385,663 Wade Sept. 25, 1945

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