US3588773A

US3588773A - Explosive circuit interrupting device

Info

Publication number: US3588773A
Application number: US816538A
Authority: US
Inventors: Charles H Carothers
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-04-16
Filing date: 1969-04-16
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28

Abstract

A CIRCUIT INTERRUPTING OR DISCONNECTOR DEVICE FOR LIGHTNING ARRESTERS COMPRISING A BREAKABLE INSULATING HOUSING ADAPTED TO BE SECURED TO ONE END OF AN ARRESTER, OR ATTACHED SEPARATELY TO AN ARRESTER, THE HOUSING SUPPORTING A GROUND TERMINAL MEANS THEREIN. THE GROUND TERMINAL MEANS IS PROVIDED WITH A RECESS FOR RECEIVING AND HOLDING AN EXPLOSIVE CHARGE IN THE

HOUSING IN SPACED RELATION THEREWITH TO FORM A SPARK GAP THEREBETWEEN. A RESISTOR IS ELECTRICALLY CONNECTED ACROSS THE SPARK GAP, THE SPACING OF THE GAP BEING SET BY AN INSULATING SLEEVE DISPOSED IN THE RECESS AND ABOUT THE CHARGE.

Description

United States Patent 72] inventor Charles H. Carothers Bloomington, Ind. [21] Appl. No. 816,538 [22] Filed Apr. 16, 1969 [45] Patented June 28, 1971 [73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

[54] EXPLOSIVE CIRCUIT INTERRUPTING DEVICE 2 Claims, 2 Drawing Figs.

[52] US. Cl. 337/30 [51] Int. Cl. "H01h 39/00 [50] Field of Search 337/28, 30;

[56] Relerences Cited UNITED STATES PATENTS 3,l00,246 8/ i963 Riley 337/30 2,824,928 2/1958 Hcdlund 337/30 FOREIGN PATENTS 706,502 3/1965 Canada 337/30 Primary Examinerl-larold Broome Assistant Examiner- Dewitt M. Morgan Attorneys-A. T. Stratton, F. P. Lyle and Elroy Strickland ABSTRACT: A circuit interrupting or disconnector device for lightning arresters comprising a breakable insulating housing adapted to be secured to one end of an arrester, or attached separately to an arrester, the housing supporting a ground terminal means therein. The ground terminal means is provided with a recess for receiving and holding an explosive charge in the housing in spaced relation therewith to form a spark gap therebetween. A resistor is electrically connected across the spark gap, the spacing of the gap being set by an insulating sleeve disposed in the recess and about the charge.

The invention relates generally to excess voltage protection devices such as lightning arresters, and particularly to a disconnect device for said arresters.

In U.S. Pat. No. 3,291,937 issued Dec. 13, 1966 to Carothers and Bo'gner, and assigned to the present assignee, there is disclosed a dropout or circuit interrupting device employing an explosive charge positioned in a molded housing supporting a ground terminal, and in a resistance coil to be heated thereby if and when associated arrester components become damaged. The damaged components conduct abnormal follow and fault current to ground through the coil, this current flow heating the coil, which in turn, heats the charge to its explosion temperature. The resulting explosion breaks the molded housing thereby interrupting the arrester circuit by dropping the ground terminal and lead.

The patented dropout device or disconnector briefly describedabove has certain disadvantages which the present disclosure avoids. Firstly, arms of a nut or fastener as one electrode of a spark gap shunting the explosive charge, the fastener being seated on a bottom wall portion of the molded housing. This, the size of the the patented device employs the gap is dependent upon flatness of the bottom wall portion and the length of the arms of the fastener, both of which vary from item to item. For example, the fasteners are generally inexpensive items that are mass produced without the quality control necessary to insure identical arm lengths for each fastener made, Such structures do not pennit accurate control of the spark gap to provide consistent sparkover voltage level for each dropout device made. For this reason, the spark gap spacing is alsosmaller, which, in turn, increases the possibility of shorting the gap.

A second disadvantage with the patented device lies with the use of the heating coil which is connected in parallel with the spark gap. The resistance (impedance) of the coil is dependent upon the frequency of the current surge being handled by the device, which, like the nut, adversely affects the consistency of the sparkover characteristic of the gap. Further, the coil tends to increase the time it takes for the dropout device to operate since the coil must first be heated and then transfer its'heat to the charge to detonate the same. For this reason, the patented device employs a primed charge to assist in the firing thereof.

BRIEF SUMMARY The present invention provides a dropout device having none of the disadvantages described above, and many advantages of its own. The invention comprises the use of an insulating sleeve and spacer to support a metal case or cartridge cont ining an unprimed explosive charge in the recess of a ground terminal, the metal cartridge having a head or flange portion which overhangs an adjacent portion of the ground terminal in spaced relation thereto to form a spark gap therebetween. The head of the cartridge is placed in electrical contact with an associated lightning arrester, and a simple resistor is electrically connected across the gap between the cartridge head and the ground terminal.

With such a structure, the spacing of the spark gap is closely controlled by closely controlling the dimensions of the sleevespacer, and the resistance of the resistor provides a fixed, nonfrequency dependent resistance value which, with the controlled sleeve-spacer, provides a consistent sparkover voltage for the gap. In the invention, the coil is eliminated, it being replaced by the resistor for leakage current passage, and the metal mass of the cartridge is heated directly by the sparking taking place between the flange of the cartridge and the ground tenninal when the arrester conducts fault current. Thus, the current-time characteristic of the invention is improved over that of the patented device, i.e., the device disclosed herein provides faster operation. And since the cartridge is heated directly, an unprimed charge may be used thereby providing a safer device for assembly, shipment and installation purposes. .An unprimed charge can be fired only by heat; it cannot be fired by impact.

THE DRAWING The invention with its advantages and objectives, will be more apparent from consideration of the following detailed description taken in connection with the accompanying drawing in which:

FIG. 1 shows an enlarged cross-sectional view of a disconnector device constructed in accordance with the principles of the invention; and

FIG. 2 is a top plan view of an insulating sleeve and spacer employed in the disconnector device of FIG. 1.

PREFERRED EMBODIMENT Specifically, in FIG. 1 there is shown a disconnector device 10 secured to an annular metal plate or cap means 12 attached to and closing the bottom end of an arrester housing 14 only partially shown. The top of the disconnector can also be sealed with a separate cap with means (not shown) for then attaching the assembly to the arrester. The cap is sealed thereto, for example, by a solder fill 15 disposed between the housing and cap. The housing contains arrester components (not shown), such as nonlinear resistance blocks and main spark gaps, in the manner well known in the art.

The disconnector device I0 comprises a breakable insulating housing 16 having a central bore 18 for receiving an end portion 20 of a ground terminal member 21. The ground terminal is secured in the housing by a nut or fastener 22 slipped over the end portion 20 and in a manner to engage the bottom wall portion of the housing. The housing is secured to the cap 12 by an integral annular portion 23 of the cap extending around and under an upper portion of the housing as shown in FIG. 1.

The insulating housing 16 is sealed to the cap 12 by virtue of an O-ring 24 disposed between the cap and the cap engaging surface of the insulating housing. In a similar manner the ground terminal 21 is sealed to the housing 16 by an O-ring 25 disposed therebetween, the O-

rings

24 and 25 being representative of other sealing means that may be used if desired. The terminal member is provided with a threaded stud 26 for securing a ground lead (not shown) to the member to electrically connect the member to ground.

In accordance with the invention, the terminal 21 is provided with a center recess 28 shaped and dimensioned to receive an insulating sleeve and spacer member 29, the sleeve and spacer being adapted to hold a metal case or cartridge 30 in spaced relation to the metal of the ground terminal. The cartridge is provided with a head and a flange portion 31 which extends in a radially outwardly direction over the end of the terminal portion 20 in spaced relation thereto to form an annular spark gap 33 therewith.

The sleeve-spacer 29 is further provided with an annular flange or disc portion 35 extending in a radially outwardly direction and into the space and plane of the spark gap 33. The spacing of the spark gap is set by the thickness of the flange portion 35. The flange portion, in turn, is provided with a pie-shaped open portion 36 as best seen in the view of FIG. 2. The flange portion may take the form of a separate insulating disc or washer disposed atop of the spacer-sleeve 29.

The head of the cartridge is placed in electrical contact with the arrester (as represented by 14 in FIG. 1) by a metal spring 38 looped through a flat insulating spacer 39 disposed between the cartridge head and the metal cap 12 of the arrester.

A simple resistor 40 is electrically connected across the spark gap 33 by having one lead connected to the spring 38 and the other lead secured to the ground terminal 21 by the nut 22.

The operation of the disconnector device 10, as thus far described, is as follows. When the components in the arrester 14 are not damaged and a surge of current is conducted to the disconnector device by said components, two possible paths to ground are provided by the device, namely a path through the resistor 40, and a path across the gap 33, the cartridge flange 31 and the ground terminal portion 20 functioning as gap electrodes. With only the initial and small portion of the surge current flowing through the resistor, the resistance thereof instantly provides a voltage drop thereacross which causes the air in the gap 33 to ionize, i.e., to establish a discharge are. The surge current, therefore, is discharged to ground across the gap. The power-follow current, having a duration of less than one-half cycle, also flows to ground through the arc across the gap. The main gap or gaps in the arrester then interrupt the power-follow current. The mass of the cartridge metal is sufficient to prevent the powder contained therein from reaching its ignition temperature when the dropout device is called upon to discharge only surge and normal power-follow currents, which occurs when the arrester 14 is working properly.

The resistor 40 provides a path to ground for leakage currents which might otherwise cause arcing across the gap 33, such arcing producing radio interference noise. The resistor is, however, protected from the major portion of surge current by operation of the spark gap 33.

When the components in the arrester 14 are damaged, the surge and first half-cycle of power-follow current are discharged in the manner described above. However, the normal 60 cycle currentflow is not interrupted by the arrester components so that it continues to flow through the arrester to the disconnector device 10. The voltage drop across the resistor 40 remains sufficiently high so that current continues to flow through to ground via the arc across the gap. The heat of the arc on the metal case 30 heats the powder contained therein to its exploding temperature. When the powder explodes, the force thereof breaks the insulating housing and interrupts the circuit of the arrester by dropping the ground terminal 21.

Since the cartridge metal is heated directly by the are between its flange 31 and ground terminal portion 20, the powder in the cartridge is ignited in a time period that is substantially shorter than that of the above described Carothers- Bogner patent. Thus, the disconnector device of the present invention has a considerably improved current-time characteristic over that of the patented device. .For this reason, the charge in the cartridge need not be primed in order to insure timely operation thereof, which in turn, pro vides a safer dropout device for assembly, shipping, and installation purposes. A primed cartridge, however, may be employed when faster operating times are required.

In order to more precisely control the arc in the gap 33, the annular flange portion 35 of the insulating sleeve 29 is provided to extend into the gap and in the plane thereof, and the flange is provided with a suitable slot or opening such as the above-mentioned pie-shaped opening 36 shown in FIG. 2.

When the arc is struck in the gap, the insulating flange concentrates the arc in the area of its open portion 36 so that the heat of the arc is concentrated to more effectively ignite the powder in the cartridge 30. Without the insulating flange, the arc would tend to develop about the cartridge in an uncontrolled manner.

It should now be apparent from the foregoing description that a new and useful disconnector device has been disclosed which overcomes certain disadvantages of the prior art in an unobvious manner. More particularly, the present disclosure provides a safe, yet quick acting explosive type disconnector device having a spark gap spacing accurately controlled by and dependent only on the thickness dimension of the sleevespacer 29 to provide for a consistent sparkover characteristic for each device. This, in turn, allows the size of the spark gap spacing to be somewhat larger than that of the Carothers- Bogner patent thereby lessening the chances of the gap becoming shorted. Though the invention has been described with a certain degree of particularity, changes may be made thirelin without departing from the spirit and scope thereof.

l. Electrical apparatus comprising: an excess voltage protective device in a housing having a metal plate closing an end thereof; a disconnector device including an insulating housing of a generally cup-shaped configuration with a rim secured to said metal plate and also having a central bore through which a ground terminal member extends; said ground terminal member having an end portion within said insulating housing, said end portion having a center recess facing toward said metal plate; an insulating sleeve and spacer member having a first portion fully lining said center recess and a second disc portion on at least part of said terminal member outside and immediately adjacent said recess; an explosive containing metal case having a first portion in said center recess spaced from said terminal member by said first portion of said insulating member, and a second flange portion outside of said center recess and extending radially outward over said terminal member and spaced therefrom by said disc portion of said insulating member; said flange portion being in electrical contact with said metal plate; said end portion of said terminal member and the periphery of said flange portion of said metal case, spaced by said disc portion of said insulating member, defining the only operative spark gap in said structure electrically between said ground terminal and said protective device.

2. The subject matter of claim 1 further comprising: a flat insulating spacer located between said metal plate and said metal case, said insulating spacer having apertures therein through which a metal spring is disposed to make'electrical contact between said metal plate and said metal case while said flat insulating spacer substantially shields said metal spring and said metal plate from said terminal member to avoid direct spark gaps therebetween; a resistor connected between said metal spring and said terminal member.