US2663817A

US2663817A - Lightning arrester

Info

Publication number: US2663817A
Application number: US243498A
Authority: US
Inventors: Val Eugene J De; Ackermann Otto
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1951-08-24
Filing date: 1951-08-24
Publication date: 1953-12-22
Anticipated expiration: 1970-12-22

Description

1953 E. J. DE VAL ET AL 2,663,817

LIGHTNING ARRESTER Filed Aug. 24, 1951 WITNESSES: INVENTORS Eugene J. DeVol and Otto Ackermonn 2M. BY

ATTOR EY Patented Dec. 22, 1953 UNITED STATES PATENT OFFICE LIGHTNING ARRESTER tion of Pennsylvania Application August 24, 1951, Serial N 0. 243,498

15 Claims. 1

The present invention relates to lightning arrosters and, more par Lcularly, to the construction of lightning arresters of the expulsion type.

Expulsion type lightning arresters consist essentially of spaced electrodes disposed in a vented arcing chamber which is lined with, or contains, insulating material capable of evolving substantially Lin-ionized gas when exposed to an electric arc. When a discharge occurs between the electrodes, a large quantity of gas is evolved which is expelled in a blast through the vent, blowing out the arc gases and deionizing the arc path to extinguish the arc, thus interrupting the power current which tends to fiOW through the arrester to ground following the discharge of a lightning surge. In the usual construction of arresters of this type, the arcing chamber consists of a tubular structure of hard fiber, or other suitable gas-evolving material, with electrodes disposed at the ends of the tube, at least one of the electrodes extending into the tube, ans at least one of the electrodes being vented. A cylindrical plug or filler of gasevolving material is usually placed in the tube between the electrodes to restrict the area of the arc path, and to increase the amount of gasevolving material exposed to the arc, in order to improve the current-interrupting ability of the arrester.

The life of an expulsion lightning arrester is determined by the severity of service, that is, the frequency and magnitude of discharges, and by the amount of gas-evolving material available to the arc and the current-limiting ability of the arrester. Each discharge uses up a small amount of gas-evolving material, and slightly increases the area of the arc path, so that the currentlimiting ability of the arrester slowly decreases in service. Ihus, the power current which the arrester will allow to flow through it gradually increases on successive discharges, and ultimately approaches the maximum system short-circuit current as an upper limit as the arrester nears the end of its useful life. The currents which the arrester must interrupt, therefore, gradually increase, during the life of the arrester, and the internal gas pressures in the arrester during oporation correspondingly increase. In the case of arresters which are installed in locations where the system short-circuit current is relatively high, the gas pressures which occur in the arrester during operation become extremely high when the arrester approaches the end of its useful life, because of the high power currents, and may become high enought to involve serious risk an expulsion type lightning arrester which has means for relieving the excessive internal gas pressures which may occur near the end of the arresters useful life, in order to prevent any risk of explosion of the arrester.

A further object of the invention is to provide an expulsion type lightning arrester in which one electrode is held in position by a simple securing means which can readily be designed to release the electrode upon the occurrence of a predetermined pressure within the arrester, thus permitting the electrode to drop off and relieve the pressure.

A still further object of the invention is to provide an expulsion lightning arrester in which one electrode is adapted to be released from the arrester at the end of the useful life of the arrester, to prevent any possibility of bursting or explosion of the arrester, and to provide an easily observed indication that the arrester is worn out and should be replaced.

The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawing, the single figure of which is a vertical sectional view of a lightning arrester embodying the invention.

The lightning arrester shown in the drawing is an expulsion type arrester having a tube or tubular structure which is preferably made of hard fiber, or other suitable insulating material capable of evolving substantially un-ionized gas when exposed to an electric are. An upper electrode 2 is disposed in the upper end of the tube l. The electrode 2 is shown as a steel sleeve which fits tightly in the tube I and is threaded in the tube l at its upper end, in order to hold the electrode rigidly in place against the strong axial thrust which occurs when the arrester operates. A lower electrode 3 is provided at the lower end of the tube I. The electrode 3 is shown as a generally cylindrical steel member which fits against the lower end of the tube I, and which is provided with a plurality of vent openings 4 for the discharge of the gas generated in the arrester during operation.

A steel sleeve 5 fits tightly over the outside 3 of the tube I to provide mechanical reinforcement for the tube against the high bursting pressures which occur during operation, and to function as an electrostatic shield to improve the spark-over characteristics of the arrester. The tube 1 has a plurality of annular grooves or depressions in it, and the sleeve is rolled or crimped into these depressions, as indicated at 6, to hold the sleeve in position and prevent relative axial movement between the sleeve and the tube. The sleeve 5 is also utilized to retain the lower electrode 3 in position at the lower end ofthe tube I. For this purpose, the electrode 3 has an annular recess or groove 1 extending around its outer surface, and the sleeve 5 is crimped or rolled into this recess, as indicated at 8, to engage the electrode 3 and hold it securely in'place against the lower end of the tube I.

In accordance with the present invention, the

lower electrode 3 is to be released from the tube 1 upon the occurrence of an excessive pressure within the tube, to relieve the pressure. This result is obtained by securing the electrode 3 in place by a pressure-sensitive securing means, and tin-the illustrated embodiment of the invention, sucha securing means is provided by the engagement between the shield 5 and electrode 3 just described. Thus, under normal conditions, the electrode 3 is tightly held-in place against the tube -l,but when an internal pressure in excess of a predetermined value occurs, the axial force applied to the electrode '3 becomes sufiicient to cause the sleeve 5 to release it. This action may occur by the crimp 8 of the sleeve springing out of the annular recess 1 to release the electrode, or the sleeve 5 may rupture at the weakened section formed by the crimp 8. Either type of action may be obtained by properly proportioning -the groove l and the crimp 8.

A generally cylindrical plug or filler member 9 of insulating, gas-evolving material such as hard -fiber' is preferably disposed in the bore of the tube l between the electrodes 2 and 3. Any suit- --able type of nllermay be used'butit is preferred -to utilize the type of filler disclosed and claimed inthe copending application of E. J. De Val, Serial No. 1 82,994, filed September 2, 1950, and assigned to the Westinghouse Electric Corporation. As more fully explained in that application, the filler 9 is generally cylindrical and has a helical groove In in its surface extending from end to end of the filler. The filler is preferably loose in the tube land rests on the lower electrode 3. -This typeof filler is very desirable because it ;causes the arc to be forced into a helical path, elongating the arc and increasing the arc voltage, thus giving the arrester a strongly currentlimiting characteristi and facilitating interruption of the arc. It is to be understood, however, that any suitable type of filler, either loose or fixedin position, may be used, if desired.

The expulsion tube assembly is contained in a generally cylindrical housing ll of porcelain, or other suitable weather-resistant insulating material. The'lowerend of the housing H is closed by a steel washer l2 which engages an external shoulder on the lower electrode 3 and is clamped against an internal shoulder in the housing i l, a "gasket 13 being interposed between the washer and the housing to seal the housing. The washer I2 has an extending lug M at one side which carries a terminal devicel5, of any suitable type, for connection of a ground'lead to the lower electrode 3. The lug I 4 is preferably bent downward,

as 'shown,'sufficiently so that the terminal 15 is substantially enclosed within the lower end of the housing I, an opening or recess i6 being provided in the housing to permit access to the terminal I5.

A series spark gap is always used with expulsion lightning arresters to isolate the arrester from the line 'undernormal conditions. =Any suitable type of gap device may be used with the arrester of the present invention, and the drawing shows a semi-enclosed gap of the type disclosed and claimed in a copending application of E. J. De Val, Serial No. 243,497, filed August 24, 1951. This gap device is contained in a porcelain housing having a lower member I! and an upper member |8,-g1azedor otherwise permanently joined together. A lower electrode member I9 is threaded on a stud-2i! which extends through a central opening in the lower housing member I! and is clamped to the housing by a nut 2|. The lower end of the stud 2D is threaded in a tapped hole in the upper end of the electrode 2 to secure the gap housing in place and to effect electrical connection between the electrodes 2 and I9. It'will be seen that when the stud 20 is tightened, the gap housing is firmly secured in place on top of, and closing, the housing H, a gasket 22' being interposed between the housing ii and the. gap housing 'to seal the housing 'I l. The washer I2 is also drawn up tightly against the lower end of the housing H to clamp the entire assembly together.

The upper electrode of the series gapcon'sists of a stud 23 extending through a central opening in the upper gap housing member i8 to "form a spark gap with the lower electrode !9. The stud '23 is accurately positionedto obtain the desired gap spacing by means of a 'U-shaped retaining member 2 3 which engages in a slot'in one'side'of the stud 23 and is seated in a recess in the housing member '18, a nut 25 being threaded on the upper end of the stud 23 to secure it in place. The upper gap housing part 18 has large openings 2B in its sides adjacent the gap, so that the gap is sufficiently enclosed to prevent accidental bridging or contact but is accessible for inspection, as more fully explained in the above-mentioned copending application. Terminal means '21 of any suitable type'are provided on the upper-end of the stud 23 to provide for attaching a line'lead'to the arrester.

In operation, when a lightning surge, or other excess voltage surge, occurs on the line "to which the arrester is connected, the gaps between 'the electrodes 2 and 3 and the electrodes 19 and 23 I and slightly'decreases the current-limiting ability of the arrester by "enlarging the area of the arc path, so that on successive discharges the power current which will flow through themrester slowly becomes larger. The gas pressures within'the arrester correspondingly increasewith successive discharges, and after a large number of discharges, as the arrester'h'e'arstheend'of its useful life; when'its 'current limiting' ability has been substantially reduced," very high gas'pressures may occur, so that there is substantial risk of the arrester bursting with explosive force. The gas pressures are highest in the neighborhood of the upper electrode 2, since the venting action of the vent openings 4 does not substantially relieve the gas pressure at the upper end of the tube Within the brief time of a discharge. These high gas pressures cause a strong axial force to be applied to the lower electrode 3 through the filler 8. As previously explained, the securing means which secures the electrode 3 in place is designed to be responsive to the pressure within the tube, and when the internal pressure during a discharge reaches a predetermined value, which is the maximum safe pressure that can be permitted to occur, and which indicates that the arrester has substantially reached the end of its useful life, the electrode 3 is released by the sleeve 5, either by rupture of the sleeve or by the crimp 8 springing out of the recess 1, as previously explained. The electrode is thus allowed to fall off and the filler 9 drops out, so that the internal gas pressure is immediately relieved and the risk of explosion is avoided. The electrode 3 will drop off and hang from the ground lead which is atg tached to the terminal 15, and since this condition can readily be seen from a considerable distance, a reliable and easily observed indication is provided to show that the arrester is worn out and must be replaced.

It should now be apparent that a construction has been provided for expulsion lightning arresters which positively prevents any risk of explosion of the arrester as it nears the end of its useful life. A particular embodiment of the invention has ben shown and described for the purpose of illustration, but it will be apparent that various other embodiments and modifications are possible within the scope of the invention, and it is to be understood, therefore, that the invention is not limited to the specific details of construction shown and described, but in its broadest aspects it includes all equivalent embodiments and modifications which come Within the scope of the appended claims.

We claim as our invention:

1. A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric arc, electrode means disposed at the ends of said tubular structure to establish an internal discharge path within the tubular struc" ture, at least one of said electrode means being vented, and means for securing the electrode means in position, the securing means of at least one of the electrode means being adapted to en- "position, the securing means of the vented electrode means being adapted to engage the electrode means to retain it in place and to release the electrode means in response to a predetermined internal pressure within the tubular structure.

3. A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric arc, electrode means disposed at the ends of said tubular structure to establish an internal discharge path within the tubular structure, at least one of said electrode means being vented, and a conducting reinforcing and shielding member on the outside of the tubular structure, said shielding member engaging one of the electrode members and retaining it in position,

4. A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric arc, electrode means disposed at the ends of said tubular structure to establish an internal discharge path within the tubular structure, at least one of said electrode means being vented, a conducting reinforcing and shielding member on the outside of the tubular structure, said shielding member engaging one of the electrode members and retaining it in position, and said shielding member being adapted to release said electrode member in response to a predetermined internal pressure within the tubular structure.

5. A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric arc, electrode m mbers disposed at the ends of said tubular structure to establish an internal discharge path within the tubular structure, at least one of said electrode members being vented, and a conducting reinforcing and shielding member on the outside of the tubular structure, one of said electrode membershaving an annular recess therein, and said shielding member extending over said one electrode member and engaging in the annular recess to retain the electrode member in position,

6. A lightning arrester comprising a tubular structure having an internal surface oi insulating material capable of evolving gas when exposed to an electric arc, electrode members disposed at the ends of said tubular structure to establish an internal discharge path Within the tubular structure, at least one of said electrode members being vented, and a conducting reinforcing and shielding member on the outside of the tubular structure. one of said electrode members having an annular recess therein, and said shielding member extending over said one electrode member and engaging in the annular recess to retain the electrode member in position, said shielding member being adapted to release the electrode member in response to a predetermined internal pressure within the tubular structure.

7. A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric are, a first electrode member extending into one end of said tubular structure and rigidly secured thereto, a second electrode member disposed at the other end of the tubular structure, at least one of said electrodes being vented, and means for securing the second electrode member in position, said securing means being adapted to engage the electrode member to retain it in place and to release the electrode member in response to a predetermined internal pressure within the tubular structure.

8. A li htning arrester compr; -ng a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to an electric are, a first electrode member 7 extending into one end of 'saidtubular strum ture and rigidly secured thereto, a secondelec trode-member disposed at the other end of the tubular structure, said second electrode member being vented, andmeans for securing the second electrode member against the end of the tubular; structure, said securing means being adapted to engage the electrode member to re= tain it in place -and to release thessecondelec trode member upon the occurrence of a predei termined internal pressure Within: the tubular structure.

9. A lightning arrester comprising a tubular structure having an internal surface of insulat ing' material capableoi evolving gas when ex posed to an electric arc, afirst electrode member extending into one end of said tubular structure and ri idly secured thereto, a second electrode member disposed at the other end of the tubular structure, said second electrode being vented, and w a conducting reinforcing and-shielding member on the outside of the tubular structure, said shielding member extending over the second electrode member and" engaging-- theelectrode member to secure it in position against th'eend of the tubular structure.

105 A lightning arrester comprising a tubular structure having an internal surface of insulating material capable of evolving gas when exposed to-an'electric arc,=a first electrode'memb'er posed to an electric arc, a'first electrode member extending into one end of said tubular structure and frigidly secured thereto; a second electrode memberdisposed at the other end of the tubular structure, said second electrode being vented, and aiconductingf reinforcing and shielding member on the outside of the tubular structure; said shielding member extendirigover the second'elec trodemember and engaging-the electrode memberto secure it in position against the end or the tubular structure; and said shielding member being adapted to release the secondelectrode member upon the occurrence of a predetermined internal pressure within the tubular structure 12.; A lightningarrester comprising a tubular structure having'an internal surface of'in'sulating' material capable of evolving gas when ex posed toan electric arc, a-first electrode member extending into one end of said tubular structure and rigidly securedfthereto, a second-"electrode member disposed at theother end or the tubular structure, saidsecond electrode member being vented and'having an annular recess therein; and

'a conducting reinforcing and'shielding member on the outside of the tubular structure; said shieldingmember extendingover the second elee structure havin'g an" internal surface of insulating.

material capable of I evolving gas-when exposed to an electric arc; electrode members disposed at the ends of saidtubular' structureto establish an internal discharge path within the tubular structure; at least on'e'of said electrode members being vented, a conducting reinforcing and shielding member fitting over the outside of the tubular structure, and means for preventing'rela= tive'axial movement between'the' shielding niei-h her and the tubular structure-,-the shieldingm em" ber extending'over one of said" electrode mem b'ers andengagi'ng said one electrode member to retain itin position. 7

14; A lightning arrester comprising a tubular structure having an internal surface of media-t: ingmaterial capable of evolving gas whenex posed to an electric arc, electrode-members dis posed at theends of said tubular structure' to establish an internal'dtscharge path-within the tubular structure, at least one of" said electrode members being vented, conducting re'i "oreing and shielding member'fitting over the on deof the tubular structure thetubular structure-hair ing an annular groove in its outer surface,- and the shielding member engaging in said groove "to prevent relative axial movement between the shielding member and the tubular structure; the shielding member extending ove'ione" ofsaid electrode members and engagingsa-idone electrode member'to retain it in positioni- 15. A lightning arres'ter cmnp'risi'ng a tubu1ar structure having an internal surface ofinsulat' ing material capable ofevolving g'as when ex-' posed to an electric arc, electrode membersdisposed at the ends of said tubular s'truc'ti'ireto establish an internal discharge path within the tubular structure; at lastone of-said" electrode members being-vented; a' conductin'g reihforcihg and "shielding member fitting over the outside or the tubular structure, thetubular' structurehaving an annular groove" in its outer surface,- and the shielding member engagingdn said groove to prevent relative axial movement between the shielding member and'the tubular structure-one of said electrode member-s having an annular recess therein; and 'the shielding member extend ingover said one electrode member and'enga'gmg in said annular reces'sto retai-n'theelectrode member in-position;

EUGENE J. DE VAL O'IT'Q AGKE-RMANN.

References Citedin the file of this patent UNITED STATESPATENTS Number Name Date 2,338,479" rl-ckerrnann Jan; 4, 1944 2,372,035 Wade a- Mar; 20, 1945 2,391,758 Wade et al Dec."25", r945