US3356808A - Circuit-interrupting devices having pressure-operated contacts - Google Patents

Description

Dec. 5, 1967 T w, DA ET AL 3,356,808 CIRCUIT-INTERRUPII'NG DEVICES HAVING PRESSURE-OPERATED CONTACTS Filed Feb. 28, 1966 3 Sheets-Sheet l ACTIVATED 5O 2o CARBON FIGJI.

L; I L2 26 H [9 SFG 50 20 ACTIVATED CARBON FIGZ.

\ INVENTORS Thomas W. Dokin Doniel Berg and Donald G. Martin M FIG.7. MflORNEY W. DAKIN ET AL Dec. 5, 1967 I CIRCUIT-INTERRUPTING DEVICES HAVING PRESSURE-OPERATED CONTACTS 3 Sheets-Sheet 2 Filed Feb. 28, 1966 CYCLES TO OPEN CIRCUIT FIG.3.

m s S P $1M C E YO P CTOO CURRENT (AMPERES) Dec. 5, 1967 T. w DAKIN ET CIRCUIT-INTERRUPTING DEVICES HAVING 3 Sheets-Sheet 3 Filed Feb. 28, 1966 IOO FIG.4.

United States Patent 3,356,808 CIRCUIT-INTERRUPTING DEVICES HAVING PRESSURE-OPERATED CONTACTS Thomas W. Dakin, Murrysville, Daniel Berg, Churchill Borough, Pittsburgh, and Donald G. Martin, Penn Township, Tralford, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, 'Pa., a corporation of Pennsylvania Filed Feb. 28, 1966, Ser. No. 530,513 11 Claims. (Cl. 200-140) ABSTRACT OF THE DISCLOSURE A gas-type circuit interrupter having pressure-responsive contacts with an electrically series arranged conducting mass of material having the characteristics of desorbing an arc-extinguishing gas upon the flow of excess current therethrough. The mass, such as activated carbon, adsorbs the arc-extinguishing gas upon cooling. Small pressure equalizing holes are provided between the pressure chamber about the separable contacts and the ballast chamber to prevent contact separation upon an increase in ambient temperature.

This invention relates generally to circuit-interrupting devices having pressure-operated contacts, and, more particularly, to circuit-interrupting devices of the aforesaid type having means for compensating for changes in am bient temperature, which would otherwise tend to effect opening of the contacts.

A general object of the present invention is to provide an improved circuit-interrupting device having activated carbon as a component element thereof, through which current is passed, which has the characteristic of desorbing gas during resistance heating by the heavy current passing therethrough, thereby eifecting pressure-opening operation of the contact structure, and in which means are provided to neutralize the effect of gradual changes of ambient temperature during operation of the device.

Still 'a further object of the present invention is the provision of an improved circuit-interrupting device having activated carbon as a component part thereof, and in which improved piston means is associated with the pressure-operated movable contact to prevent leakage past the piston portion of the movable contact, which would otherwise tend to cause faulty operation.

In US. patent application, filed Oct. 22, 1965, Ser. No. 501,180, by Daniel Berg and Thomas W. Dakin, there is disclosed and described various circuit-interrupting structures utilizing, as a component element thereof, activated carbon in conjunction with a suitable arc-extinguishing gas, in which the activated carbon adsorbs gas during cooling of the activated carbon, and in which the gas is desorbed upon heating of the activated carbon. It is a further object of the present invention to apply the principles set forth in the aforesaid patent application to a structure, which may alternately 'be used either as a protective device in a connected circuit, or as an interrupting element which is bypassed in the closed-circuit position of the device.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 is a vertical sectional view taken through an interrupting device incorporating the principles of the present invention, the contact structure being illustrated in the closed-circuit position;

FIG. 2 is a view similar to that of FIG. 1, but illustrating the position of the several parts of the device during an opening operation;

3,356,808 Patented Dec. 5, 1967 "ice FIG. 3 is a graph of the interrupting performance of the circuit interrupter of FIGS. 1 and 2;

FIG. 4 is a diagrammatic view showing the interrupting edvice of the present invention when used as a protective device in a connected circuit, and constantly carrying the series line currents;

FIG. 5 illustrates an application of the present invention to a commercial-type load-break disconnecting switch structure;

FIG. 6 is a partial vertical sectional view taken through the interrupting assembly of the load-break disconnecting switch of FIG. 5, the contact structure being illustrated in closed-circuit position; and,

FIG. 7 fragmentarily illustrates a modification of the interrupting device of FIGS. 1 and 2, the contact structure being illustrated in the closed-circuit position.

Activated carbon is generally made by carbonizing to charcoal a natural cellulosic material like coconut shell. The charcoal is then activated by steaming, or oxidizing the charcoal with air, chlorine, or zinc chloride. This process apparently opens up closed pores in the carbon structure and gives the activated carbon enormous surface area. The enormous surface area permits large weights of materials to be adsorbed on small weights of activated carbon. The size of the pores has been shown to be approximately 20 A., or larger. At the present time, all commercially-available activated carbon has pore-opening size of such dimensions that any electro-nega-tive gas, and other arc-extinguishing gases, will be readily adsorbed by the activated carbon.

The amount of material that is adsorbed depends upon the temperature and pressure of the system. The higher the temperature, the lower the amount adsorbed, and the higher the pressure, the greater the amount of gas adsorbed. Also, in comparing different molecules at the same pressure and temperature, the higher the critical temperature, the greater the amount adsorbed. The latter is qualitatively understood when it is remembered that above the critical temperature, a gas cannot be liquified no matter what the pressure. The critical temperature is a measure of the interaction between molecules, the higher the critical temperature, the greater the interaction. For a molecule to be adsorbed on a surface, it must interact with that surface. The critical temperature is a rough measure of this interaction.

It has been found that activated carbon will adsorb about 40% of its Weight of SF}; gas when the temperature is 25 C. and the pressure of SP gas is one atmosphere. On heating to about C., almost none of the SP gas remains adsorbed. On cooling, the desorbed SP gas is readsorbed. Pressures slightly greater than one atmosphere (say 2-4 atmospheres) will not cause any appreciably greater amount of SP to be adsorbed-the surface of the activated carbon is saturated. The amount of SE, gas absorbed, expressed in a volume sense, is quite large. A hundred grams of powdered activated carbon occupies roughly 200 cc. It can adsorb about 40 grams of SP gas, or about 6000 cc. of SP gas at one atmosphere. Expressed differently, the activated carbon adsorbs an amount of SP gas in a volume equivalent to compressing the SP gas to 30 atmospheres (or about 450 p.s.i.a.). As a liquid at 25 C., with a vapor pressure of 375 p.s.i., 40 grams of SP liquefied gas occupies 30 cc.

On adsorbing the SF gas, the carbon becomes warm; are taken up, or given 01f, for each grams of SP gas desorbed or adsorbed (or 33 calories per gram of SF gas).

The activated carbon is a conductor of electricity. In blocks made by binding with 20% phenolic resin, the resistivity is about 20 ohm-centimeters. This can be varied depending upon the percent carbon used, and the pressure of molding and particle size.

It has been discovered that the foregoing properties of activated carbon of adsorbing SP gas, desorbing the gason heating, and electrical conduction are extremely valuable in circuit-interrupting devices, such as lightning arresters, switchgear, circuit breakers, fuse devices, etc., as set forth in the foregoing application, in which applications the SF gas can'be held by the activated carbon and released at the proper times to extinguish the drawn arcs.

It is to be clearly understood that the present invention is not limited to the use solely of electro-negativegases, such as SF SeF and CF SF for example. The present invention is alsosuitable for use with other arc-extinguishularly outstanding and extremely effective structuresmay be fabricated using electro-negative gases, such asSF SeF CF SF for example, as the adsorbed gas. However, it will be obvious to those skilled in the art that the invention is applicable to any suitable arc-extinguishing gas, which is sutficiently adsorbed on the carbon.

FIGS. 1 and 2 illustrate a circuit-interrupting device,

generally designated by the reference numeral 10, and

incorporating principles of the present invention. It will benoted that there is provided an elongated cylindrical insulating casing 11 attached to metallic flange rings 12, 13, which, in turn are secured by a plurality of machine bolts 14 to terminal end closure plates 15, 16, to which line connections L L are made. A movable contact 18 is pressure operated, and is guided longitudinally in an insulating guidesleeve 19, which is secured interiorly of a stationary insulating enclosure cylinder 20,.the latter defining a pressure chamber 21.

As shown in FIGS. 1 and 2, the pressure chamber cylinder 20 is afi'ixed to a perforated metallic stationary contact plate 24 at one end, and to a metallic closure plate 26 at the other end. Two small pressure-equalizing holes 28, say, for example, of 5 mil size, are provided through the closure plate 26 to prevent contact separation merely because of ambient temperature changes, as ,de-

scribed more fully hereinafter.

'Sulfur-hexafiuoride (SP gas at substantially atmospheric pressure is present Within the interrupter casing 11. This is equivalentto 14.6 psi. absolute pressure of SP gas. As shown, the movable contact 18 is secured to a piston plate 30 which, in turn, is connected to a metallic pressure-operatedbellows 32.

Activated coconut charcoal 33 is confined by a 350 mesh stainless steel screen 34 preventing escape through the holes 36 of a stationary contact portion 38 of contact plate 24. In addition, a surrounding insulating tube 40 and a spring-biased contact plug 42 confine the coconut charcoal granules 33. The load current, carried by the circuit L L is used to heat the activated carbon 33 by resistance heating, and the sulfur-hexafiuoride (SP gas, which is desorbed from the activated carbon 33, creates a pressure within pressure chamber 21 to force open the contacts 18, 38 The movable contact 18 acts essentially as a pressure-responsive piston, and the inherent spring pressure of the metallic bellows 32 is compressed during interruption by the gas generated from the desorption of the SP gas from the activated carbon 33.

Important features of our invention are: use of a metallic bellows 32 in place of a coil spring, which bellows 32 provides a better pressure isolation of the two sides of the contact piston 30, and incorporation of one or more very small leak holes 28 connected between-the chambers 50, 52 on either side of the piston 30 to eliminate any sensitivity of the interrupting device 10 to ambient temperature changes.

When the switch 10 is put into the circuit L L carrying current, the current passes through the activated carbon 33, thereby heating-it. Adsorbed SP gas is released from the carbon 33 and the pressure increases within region.21.The increased, pressure tends to collapse the bellows 32, to which the movable contact 18 is connected, and to cause the contacts :18, 38 to open. If the resistance heating is sufiicient, the pressure rise will be sufficient to open the contacts 18, 38-to the-point of'arc interruption. The bellows 32-actsas a spring and guide for the contact piston .18. The chamber 50, tends to remain at constant volume during contact opening, thus offering little or no back pressure, while the volume 52 and other chambers in thedevice freely connected to 52 offer a large ballast volume which gives little back pressure.

When a bellows 32 is used, the, problem of ambient temperature changes is solved by adding an interconnecting ballast volume52 to the volume'50, which contains the contacts, by means of small diameter pressure-equalizing holes 28. The rapid pressure changes, which occur when current passes through the carbon 33, cannot be transmitted instantaneously through the small pressureequalizing holes 28, and interruption can still occur. Slow, secular pressure changes can be readily equalized through the small holes 28, and the switch 10 does not open because of slow thermal changes. As mentioned, the closure plate 26 has one or more very small holes 28 to prevent opening of the contacts 18, 38 during relatively slow heating conditions. When, however, a surge of current is caused to pass through the circuit interrupter 10, the sud- FIG. 5.

FIG. 3 is a graphof cycles to open the circuit L L as a function of the current in a-m-peres passing through the switch 10. This also demonstrates that substantial pressures ofSF can be generated by current heating of the carbon in a.cycle ortwo of 6'0-cycle current.

FIGS. 5 and 6 show theapplication of the presentinvention, as applied to a commercial loadbreak disconnecting switch, generally designated by the reference numeral 60. vAs well ,known by those skilled in the.art, the disconnecting switch 60 comprises jaw contacts .62 cooperable with the ,end .64 of aswinging movable disconnecting Switchblade 66.'Terminals 68, 7 0 electrically connectthe switch 60 into the external circuit.

.During the opening operation, a suitable mechanism disposed within a cam housing 72 causes first axial twisting of the switch blade 66 to free ice formation thereat, and to reduce contact pressure at the jaw contacts 62. Subsequently, the switch blade 66 swings in aclockwise direction, as .viewed in FIG. '5, to the fully-open circuit position, indicated by the dotted lines 74.

Upon separation of the end 64 of the switch blade ,66 from the jaws 62 of the disconnecting switch 60, the electrical circuit .will pass throughan interrupting assembly and through an upper terminal 82 to an auxiliary contact arm 84. After interruption of the circuit within element 10, as described hereinbefore, the disconnecting switch blade 66 picks up the contact auxiliary arm 84 atthe end of the opening operation. As-shown more clearly in FlG. 6 of the drawings, theinterrupting assembly 80 includes a conductor 86 interconnectingthe terminal end plate '15 with conducting housing 85 and upper terminal 82.

From the foregoing description of the invention it will be apparent that we have provided an improved circuitinterrupting element capable of being used as a protective device, and constantly connected into the series circuit L L as indicated in FIG. 4, wherein upon heavy load currents, or fa'ult currents, the device 10 will be pressure operated to the open-circuit position. Suitable disconnecting means, such as indicated by the reference numeral 1 00, may be employed in series with device 10 to maintain the circuit L L open upon the cooling of the device 10, and a subsequent reclosure of the contacts 18, 38.

More specifically, a pressure-operated relay 101, having a pressure connection 102 to the region 21, may be used to close contacts 103 thereby energizing circuit 104 through battery 105 to release latch 106 and permit compression spring 107 to open the disconnecting switch 100. This will insure that the circuit L L will not be reconnected upon subsidence of the pressure within region 21 after circuit interruption with interrupting device 10.

In addition, it will be noted that the improved interrupting element 10 of the present invention is suitable for use in a conventional-type disconnecting switch structure 60, in which the current is by-passed around the interrupting element 10 during the closed-circuit position of the device 60. During the opening operation, as pointed out hereinbefore, the current is then, and then only, sent through the interrupting element 10 to effect opening there-of by the pressure actuation of the pressure-operated contacts 18, 38.

In the interest of cost reduction, and illustrating an additional means for maintaining the circuit L L open after the device 10 operates, FIG. 7 illustrates a modified construction using a compression spring 110 and a sleeve guide 111 substituted for the metallic bellows 32 of FIGS. 1 and 2. It will be noted that the sleeve guide 111 may constitute an integral portion of metallic closure plate 26. A flexible connector 112 interconnects the contact rod 180 with end terminal plate 15. As before, pressure-equal izing apertures 28 are used together with a sealed latch rod 114 having a latching portion 114a, which is carnrned upwardly by a beveled portion 18b of the movable contact 18 during the opening operation. As a result, the contacts 1'8, 38 are latched open after the device 10 has operated. Reclosure of the contacts 18, 38 may be effected by upward manual unlatching movement of latch rod 114 as caused by grasping the external knob and pulling the same outwardly. In this embodiment, as before the movable contact 18 functions as a pressure-operated piston being immediately responsive to the pressure rise within pressure chamber 21.

In some uses of this device 10, as mentioned, it may be desirable to latch the contacts 18, 38 open. The contacts of the interrupter arrangement shown in FIGS. 1, 2 and 7 would normally be closed and would open only if a sudden high current were passed through them, causing the carbon, with adsorbed SP to be. heated. Thereafter, the carbon 33 would cool, the pressure in the contact chamber, 21, would reduce, and the contacts 18, 38 would reclose. If it were desired to keep them open, a mechanical or magnetic latch could be provided, as shown in FIG. 7, at the extremity of the open position of the contact piston, 18. This could be arranged to hold the contacts open until such time as a mechanical or electrical signal would release the latch.

Although there have been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, with-out departing from the spirit and scope of the invention.v

We claim as our invention:

1. An enclosed circuit-interrupting unit including a relatively stationary contact and a cooperable pressureoperated movable contact, a mass of confined conducting material having the characteristic of desorbing an areextinguishing gas upon the passage of excess electrical current through the said mass, means connecting said mass in the electrical circuit passing throughthe circuit-interrupting unit, whereby pressure will be generated during the passage of excess current through the unit and effect opening of the movable contact, piston means associated with said pressure-operated movable contact, means defining a ballast chamber (52) behind the piston means, means defininga pressure chamber (50) about the separable contacts and in communication with said mass of conducting material, and relatively small gas-connecting means (28) pneumatically connecting the ballast chamber with the pressure chamber to thereby prevent ambient temperature changes from effecting opening of the contacts by the equalization of the slight increase of gas pressure built up in the pressure chamber.

2. The combination according to claim 1, wherein the mass is activated carbon.

3. The combination according to claim 1, wherein a metallic bellows having inherent spring action is associated with the piston means to thereby prevent leakage into the ballast chamber.

4. In combination, means defining an enclosed interrupting unit having an arc-extinguishing gas disposed therein, an activated carbon cartridge, a stationary con-. tact and a cooperable pressure-operated movable contact, means electrically connecting the activated carbon cartridge in series electrically with the cooperable contacts, piston means associated with the pressure-operated movable contact, means defining a ballast chamber (52) on one side of the piston means and a pressure chamber (50) around the separable contacts on the other side of the piston means, means communicating the pressure chamber with said activated carbon cartridge, and means providing an ambient-temperature compensating vent (28) of small size between the ballast chamber and the pressure chamber, whereby changes of ambient temperature will not effect opening of the separable contacts by the equalization of the slight increase of gas pressure built up in the pressure chamber.

5. The combination according to claim 4, wherein the arc-extinguishing gas is selected from the group consisting of sulfur-hexafluoride (SF gas, selenium-hexafluoride (SeF gas and trifluoromethyl sulfur pentafluoride (CF SF gases.

6. The combination according to claim 4, wherein 'a metallic bellows is carried by the movable contact to prevent leakage into the ballast chamber from the pressure chamber.

7. The circuit-interrupting combination according to claim 1, wherein the piston means comprises the contactengaging portion of the movable contact and spring means is utilized to bias the contacts closed.

8. The combination according to claim 7, wherein the movable contact has a stem portion, and a sleeve guide is provided about said stem portion to assist in the guidance of the movable contact.

9. A circuit interrupter including a perforated stationary contact, a conducting cartridge connected serially in the circuit on one side of said perforated stationary contact of material having the characteristic of desorbing an arcextinguishing gas upon the passage of excess electrical current through said mass, a piston-type pressure-responsive movable contact operable with a relatively close fit within an operating cylinder (19) on the other side of said perforated stationary contact and responsive to the pressure rise of gas desorbed through the perforations of said stationary contact, means defining a pressure chamber (50) rearwardly of said movable contact, means defining a ballast chamber (52), and one or more relatively small gas-connecting means (28) pneumatically connecting the ballast chamber (52) with the pressure chamber (50) to prevent ambient temperature changes from effecting 7 8 opening the contacts by the equalization of the slight References Cited increase of gas pressure built up in the pressure chamber UNITED STATES PATENTS v 10. The combination according to claim 9, wherein the 436,045 91890 McEh'oy 4 v 1,633,521 6/ 1927 Edwards 20083 mass mated 5 3122728 6/1964 Lindberg 200-440 h l 0, h K 11 T e combination according to calm 1 w erem 3,140,368 7/1964 Young at al. 200-819 the arc-extinguishing gas is selected from the group consisting of sulfur-hexafluoride (SP gas, selenium-hexafluoride (SeF- gas and trifluorornethyl sulfur pentafluo- BERNARD GILHEANY Primary Examiner ride (CF SF gases. H. B. GILSON, Assistant Examiner.

Claims (1)

1. AN ENCLOSED CIRCUIT-INTERRUPTING UNIT INCLUDING A RELATIVELY STATIONARY CONTACT AND A COOPERABLE PRESSUREOPERATED MOVABLE CONTACT, A MASS OF CONFINED CONDUCTING MATERIAL HAVING THE CHARACTERISTIC OF DESORBING AN ARCEXTINGUISHING GAS UPON THE PASSAGE OF EXCESS ELECTRICAL CURRENT THROUGH THE SAID MASS, MEANS CONNECTING SAID MASS IN THE ELECTRICAL CIRCUIT PASSING THROUGH THE CIRCUIT-INTERRUPTING UNIT, WHEREBY PRESSURE WILL BE GENERATED DURING THE PASSAGE OF EXCESS CURRENT THROUGH THE UNIT AND EFFECT OPENING OF THE MOVABLE CONTACT, PISTON MEANS ASSOCIATED WITH SAID PRESSURE-OPERATED MOVABLE CONTACT, MEANS DEFINING A BALLAST CHAMBER (52) BEHIND THE PISTON MEANS, MEANS DEFINING A PRESSURE CHAMBER (50) ABOUT THE SEPARABLE CONTACTS AND IN COMMUNICATION WITH SAID MASS OF CONDUCTING MATERIAL, AND RELATIVELY SMALL GAS-CONNECTING MEANS (28) PNEUMATICALLY CONNECTING THE BALLAST CHAMBER WITH THE PRESSURE CHAMBER TO THEREBY PREVENT AMBIENT TEMPERATURE CHANGES FROM EFFECTING OPENING OF THE CONTACTS BY THE EQUALIZATION OF THE SLIGHT INCREASE OF GAS PRESSURE BUILT UP IN THE PRESSURE CHAMBER.

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