US 3179851 A
Description (OCR text may contain errors)
April 20, 1965 s. R. SMITH, JR
ELECTRICAL PROTECTIVE APPARATUS 3 Sheets-Sheet 1 Filed July 27, 1959 April 20, 1965 s. R. SMITH, JR
ELECTRICAL PROTECTIVE APPARATUS 3 Sheets-Sheet 2 Filed July 27, 1959 Apnl 20, 1965 s. R. SMITH, JR
ELECTRICAL PROTECTIVE APPARATUS 3 Sheets-Sheet 3 Filed July 27, 1959 United States Patent 3,179,851 ELECTRICAL PROTECTIVE APPARATUS Sidney R. Smith, Jr., Stockbridge, Mass, assignor to Generai Electric Company, a corporation of New York Filed July 27, 1959, Ser. No. 829,624 1 Claim. (Cl. 317-66) The present invention relates to electric protective apparatus including a fuse device and a lightning arrester, and more particularly-to apparatus which is provided with means for preventing the shattering or explosion of valve type lightning arresters in case of failure.
Lightning arresters of this type comprise generally a plurality of superimposed spark gap devices and a plurality of resistance elementsor blocks disposed in series relation in a housing consisting usually of a heavy insulating tube having suitable end fittings so as to be completely sealed against the entrance of moisture. The spark gaps normally insulate the arrester from the line to which it is connected but break down under excess voltage conditions such as a lightning surge to permit the surge to be discharged to ground through the resistance blocks which have low resistance under surge voltage conditions. After discharge of the surge the blocks reduce the power follow current to a small value which can readily be interrupted by the series gaps. r
During the normal operation of lightning arresters of this type no gas is generated, but it the arrester fails to interrupt the power current, the blocks lose their current limiting characteristic and the full short circuit current of the system to which the arrester is connected flows through it to ground. This results in excessive heating and arcingover whereby a high pressure is built up Within the sealed insulating housing which may cause the porcelain housing to be ruptured or shattered with explosive force causing parts of the housing to be dispersed so as to endanger adjacent apparatus or persons.
A known lightning arrester of this type is provided with a diaphragm member at each end of the tubular housing and a spacer member is disposed between the diaphragm member and the resistance blocks. The spacer member is provided with means to engage and pierce the diaphragm member when excessive pressures occur within the housing. Baffle means are fixed to the top and bottom of the housing and direct any gas escaping from the housing toward the opposite end thereof, thus forming a stream of gas which transfers the arc to the outside of the arrester thereby preventing further stress on the arrester housing.
With the current trend in arrester design to use higher rated units which are of greater physical length, the provision of practical arrangements for venting individual units when the pressure of the evolved gases becomes excessive is rendered increasingly diflicult. This is particularly true in the case where a plurality of lightning arresters are stacked together to form a multiple arrester structure. Furthermore, prior art devices of the type described above do not provide an indication of lightning arrester failure which is visible externally of the arrester housing, thus preventing a quick and easy determination of any failed arresters. It isalso easily understood that an arrangement whicheliminates the need to design the arrester in such a manner that a venting of the vaporization gases is no longer required permits the use of a lightning arrester which is simpler and more economical to manufacture.
it is, therefore, an object of the present invention to provide a protective apparatus for preventing a shattering or explosion of a lightning arrester in case of failure of the arrester.
It is another object of the invention to provide a protective apparatus in which failure of the lightning arrester causes the latter to be short-circuited by electrically con- 3,179,853. Patented Apr. 20, 1965 ductive means from a source which is external to the arrester proper.
It is a further object of the invention to provide a protective apparatus which gives an external indication when arrester failure has occurrred.
It is another object of the invention to provide an improved protective apparatus for lightning arresters facilitating the application of arrester units having greater physical length or comprising multiple arrester units.
It is an additional object of the invention to provide a protective apparatus for lightning arresters in which a bursting or exploding of the arrester is prevented without requiring a venting of the sealed arrester housing.
In the preferred form of the invention an expulsion type fuse wh ch is closed at both ends is connected in series with a lightning arrester and mounted relative to the arrester in spaced relation in such a manner that upon vaporization of the fuse element the ionized gas escaping from the fuse housing will form a conductive path to ground shunting the lightning arrester.
The invention will be better understood from the following description taken in connection with the accompanying drawing in which FIGURE 1 is a side elevational view of one form of the apparatus, partly in section;
FIGURE 2 is a schematic side elevational view of a slightly modified form of the apparatus shown in FIGURE 1 for illustrating the operation thereof;
FIGURE 3 is a side elevation of another modification, partly in section;
FIGURE 4 is a schematic view of the FIGURE 3 modification for illustrating its operation;
FIGURES 5 and 6 are similar views of a further modification.
Referring more particularly to FIG. 1 of the drawing, there is illustrated a protective device which includes a fuse device 1 connected electrically in series through a conductive strap 2 to a lightning arrester 3. The fuse device and the lightning arrester illustrated have the conventional cylindrical form and are positioned in a generally parallel spaced relationship to each other. The fuse device is of the explusion type and will not rupture when the circuit in which it is connected is subjected to steep wave front voltages but will operate upon the passage of power frequency current through the arrester. A fuse device having a circuit arrangement of this type is described and claimed in US. Patent 2,305,394, Smith, dated December 15, 1942, and assigned to the same assignee as the present invention. Another fuse device that could be suitably employed in the present apparatus is described and claimed in US. Patent 2,158,859. Horikoshi, dated May 16, 1939, and also assigned to the same assignee as the present invention It should be clearly understood, however, that the protective apparatus disclosed here is not limitedto the application of the above two particular fuse devices and that any expulsion type fuse which keeps the fuse intact when the arrester circuit is subjected to a lightning surge but which operates when the arrester circuit is subjected to commercial frequency current can be effectively used.
Referring still to FIG. 1 of the drawing, the fuse device carries at its upper end 4 line terminal 5. A line conductor 6 provides the connection of the feeder or transmission line (not shown) through fuse 1 and arrester 3 to ground. Upper end iof the fuse device is closed by a cap 7 while lower end 8 of the fuse device is closed by closure member 9. It is desirable to protect the internal elements of the fuse device from the weather and particularly in the preferred embodiment of the invention it is important to close both ends of the fuse device in order that the ionized gases generated during melting of the fuse element do not dissipate themselves prematurely. Closure 9 also constitutes or permits the provision of a signal means to indicate when the fuse has operated in response to arrester failure. For example, a flag type indicator may be used, but it is clear that other visual or audible signal arrangements may also be suitably employed.
Our invention resides in the particular application of an expulsion type fuse device provided in its preferred embodiment with closure means at both ends. The fuse device is appropriately spaced from the lightning arrester and mounted in substantially parallel relation thereto. Upon vaporization of the fusible element the closure means is opened and the ionized gases produced within the fuse housing will flow along at least a portion of the arrester housing to form a shunt circuit to ground in parallel to the arrester. The structural features of the lightning arrester and the fuse device are conventional and therefore will not be described in detail inasmuch as they are not necessary to the full understanding of the invention.
During normal operation no gas is generated in the sealed arrester housing and therefore no detrimental pressure builds up. However, if the arrester fails to interrupt power current which passes through it after a discharge, the resulting heating will lead to a breakdown of the resistance blocks and a high power are traverses the housing. The energy of the arc vaporizes the block material and the evolved gas builds up rapidly to a degree where the pressure may lead to a violent rupture of the porcelain housing.
In accordance with the present invention the building up of excessive gas pressure inside the arrester housing due to vaporization of the block material upon failure of the arrester, as well as to heating of the air or other gas normally sealed in the arrester, is prevented by providing means in the fuse device which directs a conductive means to form a parallel connection to ground to eliminate any further pressure buildup in the arrester.
In the type of fuse device described above the fuse operates when the lightning arrester fails to interrupt current of commercial frequency. The fusible element 1a is consumed or vaporized by the heat and the circuit to the arrester is interrupted in a manner well known in expulsion type fuse devices. The vaporization of the fuse element generates an ionized gas of a conducting nature. This gas escapes axially from the fuse housing in a stream 10 which contacts the arrester housing to form a current conducting path to ground as shown in FIG. 2.
According to the present invention these gases produced inside the fuse housing upon vaporization of the fuse element are expelled in a stream of sufficient density to be directed along a predetermined path into contact with at least one terminal of the lightning arrester to provide a parallel connection outside the arrester housing to divert the failure current from the arrester. Although in the preferred arrangement the fuse housing is mounted substantially parallel to the arrester housing in such a manner that the stream of ionized gas is directed into contact with the arrester column, the fuse housing may be disposed in such a manner that the stream of ionized gases may contact the arrester housing at a predetermined angle. Once a good electrical path is formed outside the arrester by the fuse gases, the current transfers from its initial path inside the arrester and thereby since no further energy would be dissipated within the arrester, any gas generation or expansion due to heat within the arrester would be stopped. Thus the build-up of excess pressure within the arrester housing would be prevented.
Referring now to FIG. 3 of the drawing, there is shown a modification of the arrangement of FIG. 2. This modification illustrates the application of a fuse device designed particularly for connection to a lightning arrester stack which comprises a relatively large number of individual arrester units. Fuse device 11 of FIG. 2 is shown mounted in series intermediate the terminals 13, 14 of the arrester stack 12 adjacent a dummy unit 15. Electrically conductive straps 16, 17 are mounted on the arrester stack 12 adjacent the dummy unit supporting the fuse device in parallel relationship to the arrester stack. Expellable caps 18 and 19 close the opposite ends of the fuse tube. It can be seen in FIG. 4 that upon failure of the arrester stack the ionized gas expelled from the fuse device 11 upon vaporization of the fusible element will form conductive gas streams 10 directed axially along the adjacent arrester stack between the axially spaced terminals 13, 14 and thus provide a parallel current conducting path on the outside of the arrester stack to ground and thereby relieve the gas pressure in the failed arrester stack.
In a further modification of the invention shown in FIGS. 5 and 6 the fuse device may be provided with a solid electrically conductive means 15 which is released or expelled from the fuse device upon rupture of the fusible element in a manner so as to provide a parallel circuit connection to ground substantially as disclosed with reference to the stream of ionized gas.
While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore, it is intended by the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
Electrical protective apparatus comprising in combination: a fuse device having an elongated housing; a lightning arrester stack having a plurality of individual arrester units, a dummy unit mounted in said arrester stack intermediate the ends of said arrester stack; said fuse device being mounted in parallel with said dummy unit and in series with said arrester units of said arrester stack; a fusible element in said fuse device; said fusible element being connected to be vaporized into ionized gas upon failure of said lightning arrester stack; said fuse device on vaporization of said fusible element expelling said ionized gas from both ends of said elongated housing of said fuse device to provide a shunt connection external to said lightning arrester stack.
References (Iited by the Examiner UNITED STATES PATENTS 893,742 7/08 Mershon 31770 2,158,859 5/39 Horikoshi 317-66 2,5 86,285 2/52 Ackerman 317-66 2,930,875 3/60 Waldvogel 200148 FOREIGN PATENTS 599,119 6/34 Germany.
765,050 1/57 Great Britain.
SAMUEL BERNSTEIN, Primary Examiner.