US2571814A

US2571814A - Lightning arrester

Info

Publication number: US2571814A
Application number: US122437A
Authority: US
Inventors: Edward F W Beck
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1949-10-20
Filing date: 1949-10-20
Publication date: 1951-10-16
Anticipated expiration: 1968-10-16

Description

0a. 16, 1951 w, BECK 2,571,814

LIGHTNING ARRESTER Filed Oct. 20, 1949 WITNESSES: INVENTOR fl/ Edward F.W.Beck.

BY iTT ZRN Y Patented Oct. 16, 1951 UNITED STATES PATENT OFFICE LIGHTNING ARRESTER Edward F. W. Beck, Pittsburgh, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October '20, 1949, Serial No. 122,437

, 3 Claims. 1

The present invention relates to lightning arresters, and, more particularly, to means for preventing shattering or explosion of valve type lightning arresters in case of failure of the arrester.

Lightning arresters of the valve type consist essentially of a plurality of spark gap devices, and a plurality of resistance elements or blocks having valve, or non-linear, characteristics, disposed in series relation in a housing. The spark gap devices normally isolate the arrester from the line to which it is connected, but upon the occurrence of an excess voltage, such as a lightning surge, the gaps break down and permit the surge to be discharged to ground through the resistance blocks, which have low resistance under excess voltage conditions. After the surge has been discharged, the blocks, because of their valve characteristic, reduce the power follow current to a small value which can readily be interrupted by the series gaps at the first current zero.

In the normal operation of lightning arresters of this type, no gas is generated within the arrester, and the housing is tightly sealed to exclude moisture, which has an adverse effect on the electrical characteristics of the gaps and valve blocks. If one or more of the blocks fails during a discharge, however, or if the arrester fails to interrupt the power current for any other reason, and thus loses its valve characteristic, the maximum short-circuit current of the system to which it is connected flows through the arirester to ground. This causes excessive heating and arcing within the arrester, and large quantities of gas are evolved from the block material. This large quantity of gas generated very rapidly 'Within the sealed housing causes very high pressures to be built up in a short time within the housing, and the porcelain housing is frequently ruptured or shattered with explosive force, in case of arrester failure, causing pieces of the porcelain to be thrown violently around, endangering adjacent apparatus or persons who may be nearby. Even if rupture of the housing does not occur, the high pressure will be held in the housing for a long period, because of the very effective sealing means used in modern lightning .arresters. This is an undesirable condition because if the damaged arrester is later opened or broken, the trapped gas may be expelled with great force.

The principal object of the present invention is to provide a lightning arrester of the valve type in which shattering or explosion of the housing,

in case of failure of the arrester, is prevented, or made less violent, by relieving the internal gas pressure.

Another object of the invention is to provide a lightning arrester of the valve type in which the housing is immediately vented upon failure of the arrester, to relieve the internal gas pressure and prevent building up of explosive pressures within the housing.

A further object of the invention is to provide a lightning arrester of the valve type in which continued arcing in an auxiliary gap device within the housing, due to failure of the arrester, causes burning or melting of a fusible element to vent the housing and thus relieve the internal gas pressure.

The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawing, the single figure of which shows a lightning arrester embodying the invention partly in elevation and partly in vertical section.

The invention is shown in the drawing embodied in a lightning arrester of unit construction, which may be used either alone or in a multi-unit assembly, with other similar units, for higher voltages. The arrester shown in the drawing is contained in a housing I of porcelain, or other suitable weather-resistant insulating material. The housing I may be closed and sealed at the top in anysuitable or usual manner, and is provided with an upper metal end casting 2,, which may be cemented to the housing I, to provide for mounting the arrester and for electrical connection to it.

The arrester elements themselves, which are disposed in the housing, comprise a plurality of spark gap devices 3, and a plurality of resistance blocks 4 of material having valve or non-linear characteristics. The spark gap devices 3 may be of any suitable type, and are shown as comprising electrode members 5 separated by annular resistance spacers 6. The electrode members 5 preferably have buttons 1 of high dielectric constant material, such as rutile ceramic, secured to them to pre-ionize the gaps to improve the surge breakdown characteristics of the gaps.

The resistance blocks 4 may be made of any suitable resistance material having valve characteristics, that is, a material which has very high resistance, or is semi-conducting, under normal conditions, but which has very low resistance under excess voltage conditions, to permit a surge to be discharged to ground with low discharge voltage across the arrester, and which is capable of again increasin its resistance after the surge has been discharged. The blocks 4 are preferably inade of granular silicon carbide mixed with a suitable binder, such as sodium silicate, and molded to the desired size and shape, and baked. Such valve blocks are, of course, well known in themselves.

The valve blocks 4 are assembled in a vertical column in the housing I, the blocks preferably being separated by spacing and centering washers 8, which may be made of relatively rigid insulating material with conducting central rivets, or other means for effecting electrical connection between adjacent blocks. The gap devices 3 are also assembled in a vertical column in the housing, in series relation with the valve blocks 4, and the column of gap devices is preferably above the column of valve blocks. The structure so far described is more Or less conventional, and is to be taken as illustrative of any lightning arrester of the valve type.

The bottom of the housing I is closed and sealed by a metal cap member 9, which may be sealed to the housing I in an suitable manner. In the construction shown in the drawing, the cap member 9 has a peripheral flange l which is soldered to a metal ring II which encircles the lower end of the housing I and is soldered to a metallic glaze on the surface of the porcelain, as indicated at I2. An annular metal bottom casting I3, having a central opening I4, is placed over the bottom of the housing I covering the cap member 9, and is cemented to the housing as indicated at I5.

The cap member 9 has a central opening l6, and a fusible element or disc I! covers the opening it and is soldered, or otherwise fastened, to the cap member 9 so as to normally close and seal :the opening [6. The disc I! may be made of lead or other suitable metal or alloy of low melting point. An annular resistance spacer I8 rests on the disc I! within the housing I, and an electrode member I9 rests on the spacer l8 and is spaced thereby from the disc H to form an auxiliary spark gap device with the disc ll. The

electrode member I9 is preferably a metal disc with a central projecting electrode portion 20,

which may be welded to the disc or formed intea metal plate 24 secured to the end casting by screws 25 to cover and protect the fusible disc H. The plate 24 is provided with a plurality of holes or openings 25 to permit escape of gas from the interior of the housing.

The normal operation of this arrester is similar to that of any valve-type lightning arrester. When a lightning surge or other excess voltage condition occurs, the spark gaps 3 break down to permit the surge to be discharged to ground through the resistance blocks 4, and after discharge of the surge the blocks reduce the power follow current to a small value which can readily be interrupted at the first current zero by the gaps. The presence of the auxiliary gap at the -bottom of the arrester does not affect the sparkover or breakdown characteristics of the arre ter, since the 60 cycle, or normal-frequency, voltage distribution across the gaps 3, is determined by the resistance spacers 6, which are in parallel with the gaps, and the impulse or surge breakdown is determined by the electrostatic field surrounding the gaps. Thus, when the breakdown voltage of the arrester is reached, the gap devices 3 break down and, in effect, cascade the auX- iliary gap to cause it to are over.

The are in the auxiliary gap, in a normal operation of the arrester, does not last for more than a half-cycle, and this brief arcing does not affect the fusible disc II. In case of failure of the arrester, however, the power current is not interrupted, and continued arcing occurs both in the auxiliary gap and in other parts of the arrester. This continued arcing in the auxiliary gap, which may be very intense because of the high current which will usually occur, rapidly burns through or melts the fusible disc I1, opening the central opening I6 in the cap member 9. Thus the housing I is vented, and the gas which is generated within the housing can escape through the opening 2| in the electrode member I9, the opening IS in the cap member 9, and the holes 26 in the plate 24. Since the fusible disc I! will be melted through very rapidly as a result of continued arcing in the auxiliary gap, the housing is vented to relieve the internal gas pressure within a very short time after failure occurs, and the gas generated within the housing is permitted to escape, so that dangerously high pressures cannot be built up in the housing, and shattering or explosion of the housing is prevented, or made less violent.

It should now be apparent that a lightning arrester of the valve type has been provided in which shattering or explosion of the housing, in

in its broadest aspects it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention: 1. A lightning arrester comprising a cylindrical housing of insulating material, a plurality of spark gap devices and a plurality of valve-type resistance blocks disposed in a column in the housing, metal cap means closing and sealing the bottom of the housing, said cap means including a central fusible element, and an electrode member below said column and spaced from said fusible element to form a spark gap therewith, the fusible element being adapted to burn through and vent the housing upon continued arcing in the last-mentioned spark gap.

2. A lightning arrester comprising a cylindrical housing of insulating material, a plurality of spark gap devices and a plurality of valve-type resistance blocks disposed in a column in the housing, metal cap means closing and sealing the bottom of the housing, said cap means including a central fusible element, a resistance spacer member resting on the cap means, and an electrode member below said column, said electrode member being spaced by the spacer member from said fusible element to form a spark gap there- 5 with, the fusible element being adapted to burn through and vent the housing upon continued arcing in the last-mentioned spark gap.

3. A lightning arrester comprising a cylindrical housing of insulating material, a plurality of spark gap devices and a plurality of valve-type resistance blocks disposed in a column in the housing, a metal cap member secured to the bottom of the housing and sealed thereto, said cap member having a central opening, a fusible element secured to the cap member to close, and seal the opening, a. resistance spacer member resting on the fusible element, and an electrode member below said column, said electrode member being spaced by the spacer member from said fusible element to form a spark gap therewith,

6 the fusible element beingadapted to burn through and vent the housing upon continued arcing in the last-mentioned spark gap.

EDWARD F. W. BECK.

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

UNITED STATES PATENTS Number Name Date 1,642,241 Golladay Sept. 13, 1927 2,179,297 Johnson Nov. 7, 1939 2,296,708 Earle Sept. 22, 1942 15 2,422,978 Olsen June 24, 1947