US3291937A - Explosive disconnect having the explosive means thermally and electrically isolated from resistance ignition means - Google Patents

Description

1 6 c. H. CAROTHERS ETAL 3,291,937

E OSIVE DISCONNECT HAVING THE EXPLUSIVE MEANS THERMALLY AND ELECTRICALLY ISOLATED FROM RESISTANCE IGNITION MEANS Filed 001;. 11, 1965 FIGI.

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5 Qk "2 4 g/34 37 bwmmmm my Q mttmctcq WITNESSES United States Patent EXPLOSIVE uiscoNivnr HAVING THE EX- PLOSIVE MEANS THERMALLY AND ELECTRH- CALLY ISOLATED FROM RESISTANCE IGNI- TION MEANS Charles H. Carothers and Philip W. Bogner, Bloomington, Ind., assignors to Westinghouse Electric Corporatron, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 11, 1965, Ser. No. 494,340 9 Claims. (Cl. 200-115) This invention relates to circuit interrupters and is particularly adaptable to interrupt fault-current and disconnect the ground lead of a lightning arrester though it is not necessarily limited thereto.

Lightning arresters of the valve type usually consist of one or more spark gaps, which isolate the arrester from the line under normal conditions but which break down and permit passage of surge currents when an over-voltage occurs, and one or more blocks of resistance ma terials having valve characteristics, that is, which are substantially non-conducting under normal voltage, but which become capable of carry-ing large surge currents when a sufficiently high voltage is applied across them. These elements are assembled in series relation in a suitable insulating casing, a suflicient number of gaps and blocks being used to obtain the desired voltage rating.

Such a device is designed to be connected between a power line and ground. When the gap sparks-over and responds to abnormal voltage, current flows from the line, through the gap assembly and then through the valve material to ground. The valve material has a high resistance at normal line to ground voltage so that the flow of power follow current after a surge has been discharged is limited in magnitude. This power follow current is then completely interrupted in the series gap at the first current zero, thus promptly restoring the ordinary non-conductive ground path to normal. Occasionally, lightning arresters become damaged and unable to interrupt the flow of follow current to ground. If the lightining arrester is unable to revert to its insulating condition, after being discharged, it places a ground on the line and causes the operation of circuit breakers, reclosers, fuse cutouts, or other protective equipment unless the lightning arrester is cleared from the circuit. If the arrester stays on the system, in its non-insulating condition, it becomes impossible to reclose the breakers, reclosers or other devices, and hence the line is locked out of service until the faulted lightning arrester has been found and removed by hand.

To combat this possibility, some types of arresters have been equipped with a so-called drop out feature or circuit interrupter. This is usually incorporated in the bottom of the lightning arrester case and the ground lead attached to it. In case of failure of an arrester the resulting heat and pressure causes fracture in a weak portion of the section at the ground end of the arrester, permitting the ground lead to drop out, thereby clearing the arrester from the circuit. Various other expedients have been resorted to for clearing lightning arresters from the line upon failure of the arrester to interrupt the power follow current on return .of the line voltage to normal. These previous expedients have included utilization of an explosive cartridge supported between a spark gap in the dropout section. In most instances the cartridge is supported in the gap so as to form a part of one of the spark gap electrodes and it is wit-h this type of expedient that this invention is generally concerned. Having the cartridge in physical and in electrical contact with the electrodes has thet particular disadvantage of subjecting the cartridge (and the explosive substance contained therein) to heating and sparking caused "by surge voltages on the line that occur from time to time during normal opera- 3,291,937 Patented Dec. 13, 1966 tion. This sparking and heating consequently causes aging of the explosive contained in the cartridge and may even cause the cartridge to explode prematurely before the arrester has actually failed.

It is therefore the object of the present invention to provide a novel circuit interrupter using an explosive charge that is not aged or otherwise adversely affected during normal operation of the circuit.

Another object of the present invention is to provide a novel drop out device for lightning arresters that is reduced in size and in cost.

Yet another object of the present invention is to provide a simple and efficient circuit interrupter that is substantially free of radio noise.

Still another object of the present invention is to provide a novel and simple expedient for relieving pressure build-up within valve type lightning arresters.

A further object of the present invention is to provide a novel and simple means for effecting an explosive drop out while isolating the explosive charge from gap electrodes,

Briefly, these and other objects of the invention are accomplished by disposing a small charge of powder, preferably a moisture sealed .22 caliber blank cartridge, or explosive rivet in a small molded housing remote from the areas of static sparking and surge current discharge, and insulated from the path of arrester leakage current. The powder is not substantially subjected to the heat generated by the sparking and leakage current and is not aged or otherwise adversely affected by the heat. This is accomplished by placing the cartridge in the center of an insulated, high resistance coil of wire that is an electrical contact with an arrester terminal means and a ground terminal means. Arrester leakage current flows through the coil to ground thereby eliminating static sparking that can cause radio interfering noise. However, with the flow of abnormal follow and arrester fault current, the high resistance coil quickly heats the cartridge powder to an explosion temperature. The resulting explosion breaks down the molded housing, and the ground lead and terminal are blown free of the arrester. During normal ope-ration of the arrester, the cartridge is substantially insulated from the working components of the arrester and drop out means.

Other objects and advantages of the will be apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevation view of an arrester incorporating the circuit interrupter of this invention;

FIG. 2 is an enlarged side cross-sectional view illustrating the circuit interrupter of this invention shown partly in elevation;

FIG. 3 is a top sectional view of the drop out assembly taken along line III-III of FIG. 2; and

FIG. 4 is an enlarged top plan view of the novel drop out assembly employed in this invention as shown in FIG. 2.

FIGURE 1 shows a typical valve type arrester device employing the unique drop out means 10 to be fully described hereinafter. The arrester includes a housing 1 made of porcelain or any other suitable type of dielectric insulating material. Housing 1 is hollow and contains the usual arrester components which include one or more resistance or capacitance graded spark gaps and one or more non-linear resistance blocks. On the top of housing 1 may be disposed a molded terminal cap 2 employed to cover a line terminal means (not shown) located on the top of the arrester housing. One the bottom end of housing 1 is secured applicants novel drop out means 10. Means 10 is secured to housing 1 by cap means 3 in a manner best shown in FIG. 2.

In FIG. 2 arrester housing 1 is centered in cap means 3 and soldered to the upper portion of cap 3 by solder fill 8 disposed around the bottom periphery of the housing. Housing 1 is further located in the center of a thin metal plate 6 and seated on annular gasket means 5. The periphery of plate 6 is provided with a flange that is secured in solder fill 8 and hermetically seals the bottom end of housing 1. Plate 6 is further provided with raised portions 7 that make electrical contact with a steel plate and a valve block (not shown) disposed in housing 1.

Drop out means 10, as best shown in FIG. 2, comprises a molded housing 12 that insulates and weather protects the internal operating components contained therein. Molded housing 12 is secured to the bottom end of arrester housing 1 by lip extension 4 of cap means 3 that is formed to fit against a flange like extension 14 of molded housing 12. Lip extension 4 is firmly pressed against molded housing portion 14 in a suitable manner which forces the top face of housing 12 against the underside of metal plate 6. Housing 12 can be sealed to plate 6 using the force exerted by lip 4 to press an O- ring disposed between plate 6 and housing 12. The O-ring is held in place by an annular groove provided in the top face of housing 12. The O-ring is shown as a sealing means for the purpose of illustration. Other means may be used in place thereof or in conjunction therewith to seal housing 12 to plate 6.

As can be clearly seen in FIG. 2, housing 12 is provided with a thin annular wall structure 16 that is shaped and designed to be rapidly and easily fractured by a force of predetermined magnitude. ther provided with a bore 18 and a clover leaf shaped depression 22 in the center thereof in which is secured the major body portion of a ground terminal stud having a clover leaf shaped shoulder portion 32 formed to fit into depression 22. The clover leaf configuration forming the shoulder portion is best seen in FIG. 3. Terminal stud 30 is inserted into housing 12 from the bottom side thereof with shoulder portion 32 and an annular extension thereof a'butted against clover leaf depression 22 and the bottom face of housing 12 respectively. Centrally located within bore 18 is a shank portion 34 of stud 30 held in place by a securing clamp or nut means 36 placed on the upper portion of shank 34. Nut holds terminal stud 30 firmly in housing 12 and against the surface face of clover leaf depression 22, thereby pressing an O-ring seal between stud 30 and an inside shoulder portion created by annular groove or depression 24 in housing 12. Thus the bottom end of housing 12 can be sealed by an O-n'ng though the invention is not limited thereto.

The shank portion 34 of stud 30 located inside molded housing 12 is cored out to provide a container for an explosive charge 40, insulating support pads 42, enamel insulated coil 44 and an insulating sleeve 46. Explosive charge may take the form of a .22 caliber blank cartridge. In FIG. 2 the cartridge is insulated at both ends from metal plate 6, metal stud 30 and end turns 45 of coil 44 by insulating pads 42 made of rubber of other suitable insulating materials. Pads 42 serve further as shock absorbers to prevent cartridge 40 from operating if the arrester is accidently dropped or otherwise jarred. The end turns of coil 44 serve both to hold pads 42 in place and make electrical contact with metal plate 6 and terminal stud 34 Thus coil 44 provides an electrically conductive path from the arrester to ground while the explosive charge remains completely insulated. Coil 44 contains an enamel coat with only ends 45 bared for electrical contact with plate 6 and stud 30.

Coil 44 is made of a high resistance type wire that is, designed to quickly heat when called upon to conduct current of any substantial quantity such as fault current. When the arrester is in good condition and operating normally, coil 44 conducts only arrester leakage current which is very small. This passing of the leakage current prevents static sparking in a spark gap formed by the ends Housing 12 is furof clamp arm extensions 39 and plate 6 making the drop out means 10 disclosed herein substantially free of radio When the line protected by the arrester and drop out 10 is struck by lightning or is otherwise subjected to surge currents, coil 44 offers a sufficient impedance to the (high frequency) surge currents so that the spark gap, formed by plate 6 and the ends of clamp arms 39, sparks over and discharges all such surges and about /2 cycle of power-follow current to ground. Immediately thereafter, the power-follow current should be interrupted at the first current zero of the alternating current cycle. If, however, the arrester is damaged and continues to conduct the line current to ground, the next half cycle and all following cycles of current transfer to the coil, since the coil has lower impedance to the low frequency cycle) current than does the gap. The "fault current quickly heats up high resistance coil 44 and causes cartridge 40 to explode. The force of the explosion breaks the molded housing thereby dropping stud 30 and a ground lead (not shown) attached thereto. The ground lead is attached to the stud by clamp means 38 and pressed against the voluted underside of stud body portion 33 by a hexagon nut threaded onto the threaded portion of stud 30.

The temperature time constant of high resistance wire 44 and the parallel gap assures little or no heating of cartridge 40 during the times of normal follow current. With abnormal follow current, however, wire 44 heats rapidly so that cartridge 40 is immediately ignited and housing 12 effectively broken apart at the thin wall portion 16 thereby removing the ground from the arrester and line.

As can be clearly seen in FIG. 2, the explosive charge 40 is completely removed from the spark gap area and discharge forming clamp electrode arms 39. Explosive charge 40, as mentioned earlier, is further completely insulated from any of the discharge forming components within housing 12. Further, no arrester leakage current is allowed to flow through charge 40 by virtue of coil 44 and insulating pads 42. Thus during normal operation of the arrester and drop out means 10, the explosive charge is thoroughly isolated from the working components. Consequently charge 40 is not heated and aged by either being subjected to sparking and discharges that occur in lightning arresters or to arrester leakage current.

High resistance coil 44 serves many functions; it conducts leakage current to ground so that cartridge 40 does not have to perform this function thereby protecting its explosive charge. Coil 44, by providing a current path to ground, eliminates static sparking between clamp elec trode 39 and plate 6 which could cause further heating and aging of the explosive charge as well as unwanted radio interference. Coil 44 is further rugged, having sufficient mechanical strength to resist physical damage both during manufacture and while performing its shunting function. Also, current tracking of the molded housing 12 over the outside surface due to external leakage current on a contaminated arrester is prevented by shunting the housing with coil 44. Thus the current flows from the cap 3 to ground stud 30 through coil 44 instead of over the outer surface of housing 12.

In the same manner clamp means 36 serves many functions. Besides securing stud 30 to molded housing 12, the upright ends 39 of clamp 36 form spark gap electrodes 'with thin metal plate 6. Further, clamp 36 performs a third function that creates an additional advantage in the unique drop out means 10 disclosed herein. As previously mentioned, plate 6 is made of a relatively thin metal. When drop out means 10 operates and housing 12 breaks, forcing clamp 36 and the other components away from plate 6, the end of the fault current arc developed between the end of clamp arm 39 and plate 6 will heat and burn a hole through plate 6. Any pressure build up inside the arrester will be vented through this hole and prevent arrester housing 1 from exploding.

In the cored out shank portion 34 of terminal stud means 30 can be disposed an insulating sleeve 46 that insulates, protects and centers coil 44 within the core.

FIG. 3 shows clearly the clover-leaf configuration provided in the bottom face of housing 12 and portion 32 of the body extension of terminal stud 30. The purpose of such a configuration is to prevent stud 30 from turning in molded housing 12 and to distribute the torque stress over a large area of cup 12 to prevent cracking when a torque force is applied thereto, such as when a lineman tightens the hexagon nut disposed on the threaded portion of stud 30 (FIG. 2). Clover-leaf depression 22 fits snugly over a like shaped shoulder portion 32 provided in the face of the lateral body extension of terminal stud 30 when the stud body is inserted into housing 12 from the bottom side thereof.

In a similar manner housing 12 is kept from turning when torque force is applied to stud 30. In FIG. 4 housing 12 is shown to be provided with four flat surfaces 15 symmetrically disposed around the edge of housing extension 14. Lip extensions 4 of cap means 3 can be firmly pressed against these flat surfaces 15 as best shown in FIG. 2. Thus such a structure resists turning so that a ground lead (not shown) may be firmly secured on the bottom of terminal stud 30 by clamp 38 and the hexagon nut immediately disposed thereunder.

FIG. 4 further shows clamping means 36 having four inwardly projecting edges 37 fitting around shank portion 34 of terminal stud 30 for the purpose of securing stud 30 to housing 12. Clamping means 36 is further shown to have two arms 39, the ends of which form spark gap electrodes with metal plate 6 sealing the bottom of arrester housing 1. The type of securing clamp 36 and the number of arm extensions 39 are shown for purposes of illustration. Other types of securing means may be used in place thereof as long as terminal stud 30 is firmly secured thereby and means are provided in housing 12 for forming a gap electrode or electrodes with arrester bottom plate 6 at a distance removed from explosive charge 40.

It should now be apparent that a unique, simple and effective drop out means has been disclosed that guarantees a surety of operation and ease of maintenance heretofore unavailable in the prior art. This is accomplished by applicants novel arrangement of inexpensive parts disposed in a small housing easily secured to the bottom of an arrester device. By disposing a .22 caliber blank cartridge outside sparking and discharging areas, and insulated from the heat generated thereby as well as arrester leakage current, the explosive powder contained in the cartridge is not aged or otherwise adversely affected thereby. Yet the powder can be efiectively and rapidly heated for explosion by a simple and inexpensive coil of wir disposed therearound when an arrester fault current is conducted therethrough. The coil further serves to conduct arrester leakage currents to ground thereby preventing static sparking within the dropout unit that can cause radio interference. Further, a simple clamping means secures a terminal stud to the drop out housing and doubles as a spark gap electrode removed from the area of the explosive charge. Clamping means further serves to provide vent holes in the arrester device when the drop out device operates. Thus such a unique construction produces the novel result outlined above in an efiicient and effective manner nowhere to be found in the prior art.

Though the invention has been described with a certain degree of particularity, it is to be understood that the disclosure herein presented has been made by way of example only and that changes may be made therein without departing from the spirit and scope of the invention.

We claim as our invention:

1. A circuit interrupter adapted to be connected in series with an excessive voltage protective device, said interrupter comprising an insulating housing secured to one end of said protective device, said housing containing an electrode means for forming a spark gap between said electrode means and the one end of said protective device, a high resistance means in electrical parallel with the spark gap supported in said housing and having one end in electrical contact with the one end of the protective device and its other end in electrical contact with a terminal means secured in said housing, an explosive means disposed in close proximity to the resistance means for rupturing the housing and removing the electrode and the terminal means from the housing upon being heated by the resistance means conducting a continuous flow of current, the explosive means being further effective to disconnect the resistance means when the terminal is removed, the explosive means being insulatingly supported in the housing so that under normal operating conditions the explosive means remains thermally and electrically isolated from the spark gap and current flow paths.

2. In combination with an arrester device having a terminal portion, an automatic circuit interrupting means comprising an insulating housing having at least one electrode mounted therein and in a position to form a spark gap with said arrester terminal portion, a high resistance heating device secured in said housing and connected in electrical parallel with said spark gap, explosive disconnecting means supported in the axial center of said device and insulated therefrom for rupturing the housing and removing said electrode and said gap from the housing upon being heated by said device under predetermined conditions of arrester current flow, said disconnecting means thermally and electrically isolated from the spark gap and current flow paths under normal operating conditions.

3. The circuit interrupter of claim 1 in which said housing is provided with a thin wall portion, and said terminal means is supported in said housing by a means forming a spark gap with said one end of said protective device.

4. A circuit interrupter having a molded housing provided with a surface depression in at least one end thereof for receiving a ground terminal means, said end surface depression having inside wall surfaces with rounded concave depressions in a plane perpendicular to the plane of the end surface depression, said terminal means having a body portion provided with convex wall surfaces fitting into said concave depressions on the inside wall surfaces of said housing end surface depression, said terminal means secured in said housing by a fastening means that forms one electrode of a spark gap in said housing, a high electrical resistance coil disposed in said housing and connected across the spark gap, an explosive disconnecting device mounted in the axial center of but insulated from the coil and terminal means, said device removing said terminal means from said housing upon being heated by said coil functioning under predetermined conditions of current flow therethrough,

5. The structure of claim 4 wherein the concave and convex surfaces form substantially a clover leaf configuration.

6. The circuit interrupter of claim 1 in which said terminal is provided with a centrally disposed depression for supporting therein said resistance means and said explosive means.

7. The circuit interrupter of claim 6 wherein the explosive means is a .22 caliber blank cartridge.

8. In combination with a line arrester device having a housing with at least one terminal portion made of a relatively thin metal material hermetically sealing said housing, circuit disconnecting means comprising an insulated housing with an electrode disposed therein and in a position to form a spark gap with said terminal portion, said insulated housing being hermetically sealed to said terminal portion of said arrester housing, a ground lead connector extending into said insulated housing and secured therein by said spark gap electrode, a high resistance coil longitudinally supported between said terminal portion of said arrester housing and said ground connector in said insulated housing, the ends of said coil respectively electrically contacting said terminal portion and said ground connector, an explosive medium disposed in the axial center of said coil but insulated therefrom the terminal portion and ground connector, said medium adapted to expel said ground connector upon being heated by said coil conducting arrester fault current, said thin metal terminal portion of said arrester housing adapted to be punctured by the heat of an are produced by said fault current as the ground connector is being expelled, said puncture venting to the outside atmosphere any gas pressure build-up within the arrester housing.

9. A circuit interrupter comprising an insulating housing containing a spark gap, an electrical resistance heating means connected in electrical parallel across the gap, an explosive means for disconnecting the circuit disposed gap and resistance means under normal operating conditions and current flow.

References Cited by the Examiner UNITED STATES PATENTS 1,568,069 1/1926 Jenkins 10228 2,481,696 9/1949 Seavey 10228 2,989,608 6/1961 Hicks 2001l5 3,177,322 4/1965 Shaw -s 102-28 X BERNARD A. GILHEANY, Primary Examiner.

H. A. LEWITTER, Assistant Examiner.

Claims (1)

1. 9. A CIRCUIT INTERRUPTER COMPRISING AN INSULATING HOUSING CONTAINING A SPARK GAP, AN ELECTRICAL RESISTANCE HEATING MEANS CONNECTED IN ELECTRICAL PARALLEL ACROSS THE GAP, AN EXPLOSIVE MEANS FOR DISCONNECTING THE CIRCUIT DISPOSED IN CLOSE PROXIMITY TO THE RESISTANCE MEANS, THE RESISTANCE MEANS ADAPTED TO IGNITE THE EXPLOSIVE MEANS UPON BEING HEATED BY A CONTINUOUS FLOW OF CURRENT, THE EXPLOSIVE MEANS BEING ADAPTED TO RUPTURE THE HOUSING AND TO REMOVE AN ELECTRODE FORMING THE GAP FROM THE HOUSING, THE EXPLOSIVE MEANS BEING FURTHER EFFECTIVE TO DISCONNECT THE RESISTANCE MEANS CONNECTED ACROSS THE GAP, THE EXPLOSIVE MEANS BEING THERMALLY AND ELECTRICALLY ISOLATED FROM THE GAP AND RESISTANCE MEANS UNDER NORMAL OPERATING CONDITIONS AND CURRENT FLOW.

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